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>> HELLO.
WELCOME TO TODAY'S WEDNESDAY AFTERNOON
LECTURE AT NATIONAL INSTITUTES
OF HEALTH.
THANK YOU FOR COMING.
MY NAME IS JUSTIN TERASKA.
I'M AN INVESTIGATOR IN THE
LABORATORY OF MOLECULAR
BIOPHYSICS IN THE NATIONAL HEART
LUNG AND BLOOD INSTITUTE.
IT'S MY PLEASURE TO INTRODUCE
DR. JAMES ROTHMAN AS TODAY'S
WALS SPEAKER.
DR. ROTHMAN IS WALS PROFESSOR OF
BIOMEDICAL SCIENCES AND CHAIR OF
DEPARTMENT OF BIOMEDICAL AT
YALE.
HE'S ONE OF THE MOST INNOVATIVE
AND INFLUENTIAL CELL BIOLOGISTS
AND BUY CHEMISTS WORKING OFFER
THE LAST FEW DECADES.
DURING TENURES AT STANFORD,
PRINCETON, INVENTORY DEBT R,
COLUMBIA AN YALE, -- CLONE
KETTERING AND YALE, THIS IS
INCLUDED SEMINOLE DISCOVERIES
RELATED TO HOW PROTEINS INSERT
INTO MEMBRANES.
HOW VESICALES TRAFFIC THROUGH
THE CELL, AND HOW VESICALES FUSE
WITH THE MEMBRANE, A PROCESS
CALLED EXOCYTOSIS.
ASIDE FROM THE BIOLOGICAL
DISCOVERIES HIS LAB HAS INVENTED
IMPORTANT METHODS INCLUDING IN
VITRO RECONSTITUTION OF VESICAL
TRAFFICKING PATHWAYS WHICH HAS
REALLY ALLOWED THE COMPLEX STEPS
OF VESICAL TRAFFICKING TO BE
TEASED APART AT THEIR MOST
FUNDAMENTAL LEVEL H.
ADDITIONALLY DEVELOPED NOVEL PH
FLUORESCENCE PROTEINS THAT ALLOW
INDIVIDUAL SYNAPSES AND SINGLE
VESICALES TO BE WATCHED IN
LIVING CELLS IN REAL TIME.
IN PARTICULAR, DR. ROTHMAN HAS
HELPED TO ESTABLISH THE SNARE
HYPOTHESIS OF MEMBRANE FUSION
WHICH PROPOSES THAT THE CORRECT
PAIRING OF ALPHA HELICAL
PROTEINS ON TWO OPPOSED
MEMBRANES DIRECTS AND CATALYZES
THEIR FUSION.
ALONG WITH THESE IMPORTANT
DISCOVERIES DR. ROTHMAN MENTORED
AND TRAINED MANY PROMINENT
SUCCESSFUL BIOCHEMISTS AND CELL
BIOLOGISTS.
HE'S A MEMBER OF THE NAB
NATIONAL ACADEMY, INSTITUTE OF
MEDICINE AND RECIPIENT OF
NUMEROUS AWARDS INCLUDING LASTER
AWARD FOR BASIC SCIENCE AND
CAVALI PRIZE FOR NEUROSCIENCE.
HE WILL DISCUSS HIS RECENT WORK
ON SNARES AND THE ACCESSORY
PROTEINS THAT DIRECT THEIR
FUSION.
IN A TALK TITLED MOLECULAR
MECHANISMS OF SYNCHRONOUS
NEUROTRANSMITTER RELEASE. AFTER
THE SEMINAR THERE WILL BE A
RECEPTION IN THE LIBRARY SO
PLEASE COME AND THEY'LL GIVE YOU
AN OPPORTUNITY TO SPEAK MORE
INFORMALLY WITH DR. ROTHMAN.
JOIN ME GIVING A WARM WELCOME TO
JIM ROTHMAN.
[APPLAUSE]
>> THANK YOU.
THANKS FOR ARRANGING THE DAY,
BEING A GREAT HOST AND ALSO
SHARING WITH ME YOUR RECENT AND
EXCITING WORK especially on
novel methods used Ford
measuring confirmational changes
in proximity with fret.
IT'SER EXCITING, I HOPE WE CAN
COLLABORATE AS A RESULT OF THAT.
PLEASURE TO BE HERE WITH YOU
TODAY.
I'M GOING TO AS THE TITLE
SUGGESTS, TALK ABOUT THE PROCESS
OF SYNCHRONOUS NEUROTRANSMITTER
RELEASE.
THERE'S BEEN A LOT OF PROGRESS
OVER THE LAST FIVE YEARS I WOULD
SAY ESPECIALLY IN BEGINNING TO
UNDERSTAND THE MECHANISM BY
WHICH THIS VERY IMPORTANT
PHYSIOLOGICAL PROCESS OCCURS IN
STRUCTURAL AND BIOCHEMICAL
TERMS.
SO WHAT I WOULD LIKE TO DO TODAY
IS OFFER SOME HISTORICAL
BACKGROUNDS TO THE THE PROBLEMS
AND THEN AFTER THAT SHARE WITH
YOU OUR CURRENT VIEW IN THE FORM
OF A MODEL OF HOW A SYNCHRONOUS
TRANSMISSION NEUROTRANSMITTER
RELEASE MAY WORK.
A STRUCTURAL BUOY CHEMICAL MODEL
AND AFTER THAT SHOW YOU SOME OF
THE EVIDENCE ACCUMULATED FOR THE
MODEL OVER THE LAST TWO OR THREE
YEARS ESPECIALLY.
WHAT DO I MEAN BY SYNCHRONOUS
NEUROTRANSMITTER RELEASE?
IT'S ACTUALLY THE PHYSIOLOGISTS
HAVE VARIOUS COMPLEX SCHEMES TO
MEASURE IT AND WAYS OF DEFINING
IT.
TO ME IT'S VERY SIMPLE BUT
FUNDAMENTAL CONCEPT IN
NEUROSCIENCE WHICH IS WHEN THE
ACTION POTENTIAL COMES DOWN THE
END OF THE NERVE AND YOU RELEASE
A NEUROTRANSMITTER ACROSS A
SYNAPSE TO THE NEXT NERVE OR
PERHAPS MUSCLE CELL, THE
NEUROTRANSMITTER NEEDS TO BE
RELEASED AT THE RIGHT TIME.
WE DIDN'T WANT THE
NEUROTRANSMITTER TO BE RELEASED
ASYNCHRONOUSLY ON ITS OWN ACCORD
BECAUSE IN THAT CASE IT'S A
FALSE ALARM.
YOU ALSO DON'T WANT THE
NEUROTRANSMITTER TO GO NOT BEING
RELEASED BECAUSE YOU MISSED AN
IMPORTANT SIGNAL.
IN FACT WHAT YOU WANT, YOU WANT
THE NEUROTRANSMITTER TO BE
RELEASED PRECISELY SYNCHRONOUSLY
WITH THE ARRIVAL OF ACTION
POTENTIAL AT SYNAPTIC TERMINAL.
THE WAY THAT'S ACHIEVEED IS
THROUGH MEMBRANE GATED CALCIUM
CHANNELS, PROBABLY EVERYONE
KNOWS THAT ARE LOCALIZED IN THE
SYNAPTIC PRE-SYNAPTIC REGION
THAT OPENED UP THE GATE FOR
CALCIUM ENTRY AND IT ACTS AS A
SECOND MESSENGER TO TRIGGER
RELEASE OF NEUROTRANSMITTER
STORED IN VESICALES.
THE PROBLEM THAT WE HAVE TAKEN
ON THAT I WOULD LIKE TO ADDRESS
HERE IS NUMBER ONE HOW ARE THESE
VESICLES RELEASED?
HOW DO THEY FUSE WITH THE
SURROUNDING MEMBRANE HAVING
STORED THE NEUROTRANSMITTER
WITHIN THEMSELVES.
HOW DO THEY DO IT SO RAPIDLY?
SO MUCH MORE RAPIDLY, ORDERS OF
THE MAGNITUDE MORE RAPIDLY.
THAN OTHER MEMBRANE FUSION
PROCESSES THAT TAKE PLACE IN THE
CELL.
SO THOSE ARE THE ASPECTS BUILT
INTO SIN CROW IN THISTY.
IT'S OBVIOUSLY IMPORTANT AT A
GROSS LEVEL.
IN YOUR BRAIN IF YOUR
NEUROTRANSMITTERS WERE RELEASED
HEALTHER SETTLER, THERE WOULD BE
NO POSSIBILITY OF C9
INFORMATION PROCESSING OR
ANYTHING OF ANY REMOTE INTEREST.
YOU WOULD HAVE A -- THINK ABOUT
WHAT EXPERIENCE WOULD BE IF YOUR
VESICALES ALL FUSED AS THEY
SHOULD BECAUSE THE FUSION
PROTEINS ARE CONSTITUTIVELY
ACTIVE.
THEY SHOULD FUSE AND RELEASE
NEUROTRANSMITTER ALL AT ONCE SO
THEN YOU HAVE EVERY
NEUROTRANSMISSION TAKING PLACE
AT ONCE WITHIN A SHORT PERIOD OF
TIME, NO THOUGHTS WHATSOEVER OR
PERHAPS EVERY THOUGHT YOU WOULD
HAVE AND NOT BE ABLE TO
COMMUNICATE TO EVERYONE ELSE, IT
MIGHT BE AN INTENSELY
TRANSFORMATIONAL EXPERIENCE BUT
IT WOULD BE ONE THAT LASTS 10
MILLISECONDS.
SO THAT CLEARLY DOESN'T HAPPEN.
IN A MUCH MORE SUBTLE LEVEL THE
SPEED OF SYNAPTIC TRANSMISSION
IS VERY IMPORTANT FOR THE
COMPLEX CIRCUITS THAT WE HAVE.
IT TYPICALLY TAKES A FEW
MILLISECONDS FOR A SIGNAL TO BE
TRANSPORTED ACROSS A SYNAPSE OF
WHICH THE RELEASE PROCESS,
INITIATION OF IT TAKES TYPICALLY
LESS THAN A MILLISECOND IN
CENTRAL SYNAPSES.
THAT'S ACTUALLY VERY IMPORTANT
BECAUSE FROM THE TIME THAT A
PRIMARY PIECE OF POTENTIAL
COGNITIVE INFORMATION LIKE
VISUAL FIELD AND AUDITORY
PATTERN WHAT HAVE YOU, IS
SENTENCED BY OUR INPUT OUTPUT
DEVICES, IT HAS MAYBE 20 OR 30
MILLISECONDS FOR ALL THOSE
PATTERNS COALESCE AT YOUR
HIGHEST CENTERS HAVING BEEN
TRANSMITTED THROUGH PERHAPS TEN
OR 15 DIFFERENT SYNAPSES.
I THINK WE'RE ALL FAMILIAR WITH
SOME ANYWAY ARE OLD ENOUGH TO
REMEMBER WHAT MOVIES USED TO BE
LIKE WHERE THE FILM GOES BY AND
YOU HAVE 35, THE MAGIC NUMBER
FRAMES PER SECOND.
WHY 35?
BECAUSE IF IT'S FASTER THAN 35
IT LOOKS LIKE A CONTINUUM TO
YOU.
IF IT'S SLOWER THAN 35, YOU SEE
SEPARATE PICTURES.
HOLLYWOOD FOLKS WEREN'T SPEND
THRIFTS THEY WERE LOOKING FOR
PROFITS, SO THEY FIGURED OUT
THAT THE GRANULARITY OF HUMAN
EXPERIENCE IS ABOUT 25 OR 30
MILLISECONDS.
SO YOU CAN GET BY WITH THE LEAST
NUMBER OF PHOTOGRAPHIC FILM AT
THAT SPEED.
SO THAT 25, 30 MILISEDGES IS
WHAT YOU HAVE THAT REPRESENTS
SIN CROW IN THISTY AND THE JOB
IS TO GET THROUGH 10, 15
SYNAPSES AND PLOW THROUGH THEM
FROM HERE AND HERE UP TO HERE.
FAST ENOUGH.
HOW DOES THAT WORK IN MOLECULAR
TERMS?
THAT'S THE PROBLEM I WOULD LIKE
TO THE ADDRESS TODAY.
THE SOLUTION TO THIS PROBLEM HAS
COME I WOULD SAY OVER SEVERAL
DECADES, ACTUALLY MORE LIKE HALF
A CENTURY, MANY WHICH CELL
BIOLOGY AND NEUROSCIENCE OR
NEUROPHYSIOLOGY AS IT WAS THEN
CALLED DOVE TAILED TOGETHER,
GONE APART COME BACK TOGETHER
AND THERE'S MANY CRITICAL COMING
TOGETHERS OF THESE TWO FIELDS.
THE BEGINNING OF THIS FIELD IN
FACT REFLECTED THAT.
GOING BACK TO THE CLASSIC WORK
OF FAT AND CAT WHO FOUND HOST
SYNAPTIC POTENTIALS, THE
NEUROMUSCULAR JUNCTION IN
CLASSICAL EXPERIMENTS FROM
1950s, IF YOU HAVE AN
ELECTRICAL IMPULSE STIMULATING
THE NERVE INNER INVESTIGATING
THE MUSCLE, WHEN YOU GET
SYNAPTIC TRANSMISSION THE
MEMBRANE POTENTIAL OF THE MUSCLE
CHANGES IN RESPONSE.
IN YOU HAVE NO INPUT NO ACTION
POTENTIAL, ON THE MUCH SMALLER
SCALE THERE'S MINIATURE
POTENTIALS OR MINIS THAT APPEAR
AT FAIRLY LOW FREQUENCY BUT YOU
CAN SEE THAT THEY'RE ABSOLUTELY
MEASURABLE AND SEEM TO BE OF
UNIFORM SIZE MEASURED AS A POST
SYNAPTIC POTENTIAL.
IN THAT CAPS THE IDEA
TRANSFORMATIONAL IDEA THAT
SYNAPTIC TRANSMISSION THE
RELEASE OF NEUROTRANSMITTERS
OKAY CANS IN A JUAN UNTIL
FASHION WHICH THERE ARE
INDIVIDUAL PACKETS OF
NEUROTRANSMITTER SOMEHOW
PREARRANGED STORED AT A NERVE
ENDING SHOWN HERE.
ABILITY THE SAME TIME IN 1950s
MY PREDECESSOR AND FOUNDER OF
CELL BIOLOGY AT YALE, THE
FOUNDER TO LARGE DEGREE FIELD OF
CELL BIOLOGY OBSERVED THESE
MEMBRANE ENCLOSED VESICALES AT
NERVE ENDINGS.
HE CALLED THESE SYNAPTIC
VESICALES.
AND HE ALSO OBSERVED VESICALES
OF MANY KINDS IN THE CELL AND
CAME UP WITH THE IDEA THAT
VESICALES ARE CAPABLE OF
MEMBRANE FUSION.
SUGGESTED THAT THESE SYNAPTIC
VESICALES ARE IN FACT STORING
THE NEUROTRANSMITTER, A JUAN
UNTIL OF NEUROTRAN MITTER AND
MADE THAT CONNECTION IN
THE VESICAL HYPOTHESIS.
THE IDEA IS THAT THESE VESICALES
FUSE AFTER STIMULATION AND IT
WAS CAPTURED DISCOVERED THAT THE
ENTRY OF CALCIUM INTO THE --
THAT'S NEURONS SYNAPSES LIKELY
PROVIDES THE IMMEDIATE TRIGGER.
MORE MODERN WORK THROUGH THE
1970s, IN FACT CONDUCTED HERE
AT NIH BY REECE AND HOUSER THIS
VESICAL HYPOTHESIS RECEIVE
STRONG SUPPORT WHERE THEY
OBSERVE VESICALES LIKE THIS, IN
FACT WERE SEEN FUSING WITH THE
PRE-SYNAPTIC PLASMA MEMBRANE
RELEASING THE NEUROTRANSMIT INTO
THE SYNAPTIC CLEFT TO DIFFUSE
ACROSS THE SYNAPSE.
HERE THEN IS ONE OF THE EARLY
COMING TOGETHERS OF CELL BIOLOGY
AND NEUROPHYSIOLOGY IN THE
VESICAL HYPOTHESIS.
THIS VIEW THAT VESICALES CAN
STORE COMPOUNDS FOR RELEASE FROM
THE CELL, WHICH AS JUSTIN SAID
GOES BY THE NAME OF EXOCYTOSIS
BUT INDEPENDENTLY REACHED AND
GENERALIZED BY PILATI AND
COLLEAGUES.
THERE ARE MUCH LARGER VESICLES
THAT STORE INSULIN OR IN THIS
CASE EXOCRINE SECRETIONS MANY
THE PANCREAS THAT ARE READY TO
BE RELEASED AND THEN ARE
RELEASED.
FOLLOWING A STIMULATION.
WHAT THIS INTRODUCES IS A
GENERAL CONCEPT WHICH IS VEST IT
WILLS STORE PRODUCTS THAT NEED
TO BE RELEASED RAPIDLY.
MUCH MORE RAPIDLY THAN THEY CAN
BE SYNTHESIZED OR LOCALIZEED TO
THE SITE OF RELEASE.
AND THAT THIS OCCURS
PHYSIOLOGICALLY.
IN NO PLACE IS THIS KINETIC
DEMAND FASTER THAN IN THE BRAIN.
FOR THE REASONS THAT I
MENTIONED.
PROBABLY SECOND FASTERS IS THE
RELEASE OVINES -- FASTEST IS
RELEASE OF INSULIN, SECONDS TO
COUPLE OF MINUTES.
MORE LEISURELY IS THE PROCESS OF
MEMBRANE FUSION AS IT OCCURS
WITHIN THE CYTOPLASM.
AND INDEED WORK IN THE 1970s,
1980s AS WE BEGAN TO DISCOVER
RANGE OF VESICALES THAT TRAVERSE
THE CYTOPLASM CARRYING CARGO BY
BUDDING AND FUSION FROM ONE
COMPARTMENT TO ANOTHER WE NOW
RECOGNIZE AT LEAST A DOZEN, SOME
SPECIALIZED CELLS PROBABLY MORE
TYPES OF VESICALES EACH SELECTS
FOR A CARGO AND NEEDS TO DELIVER
THAT BY MEMBRANE FUSION WE CAME
TO REALIZE THIS PROCESS OF
MEMBRANE FUSION IS REALLY
GENERAL.
NOT JUST WITHIN A SINGLE CELL
CYTOPLASM THERE ARE PROBABLY TEN
OR 20 IN COMPLEX EUKARYOTIC
CELLS, TYPES OF MEMBRANE FUSION
THAT OCCUR, BUT ALSO GENERAL
BIOLOGY FROM PLANTS TO MICROBES
EUKARYOTIC MICROBES AND TO
HUMANS.
SO WHAT AGAIN BY WAY OF
BACKGROUND, THIS IS ALREADY BEEN
INTRODUCED, WHAT I PERSONALLY
FIND STILL QUITE ASTONISHING IS
THAT THIS ENTIRE ARRAY OF
PHYSIOLOGICALLY IMPORTANT
MEMBRANE FUSION PROCESSES FROM
THE SYNAPSE TO HORMONE RELEASE
TO THE COMPARTMENTAL
ORGANIZATION OF THE CYTOPLASM
AND IT PROPAGATION IN CELL
DIVISION, ARE ALL RELATE TO WORK
THE HANDIWORK OF A SINGLE FAMILY
OF PROTEINS.
THIS FAMILY OF PROTEINS CALLED
SNARE PROTEINS COMES IN A NUMBER
OF VARIETIES BUT THEY HAVE IN
COMMON PHICAL CHEMICAL MECHANISM
FOR MEMBRANE FUSION.
THERE ARE TWO TYPES OF SNARE
PROTEINS PHYSICALLY
COMPLIMENTARY TO EACH OTHER, WE
CALL THEM V AND T SNARES.
THEY EXIST IN -- THEY'RE
LOCALIZED DIFFERENTLY WITHIN THE
CELL.
A V SNARE PARTNERS A T SNARE AND
BRIDGES THE GAP BETWEEN TWO
MEMBRANES, AS I'LL DESCRIBE IN
STRUCTURAL TERMS IN A MOMENT NOT
ONLY INITIATE IT IS PROCESS OF
MEMBRANE FUSION, BILAYER FUSION
BUT ACTUALLY FUSES THE
BIOLAYERS.
BUT THERE ARE MANY DIFFERENT
TYPES OF V SNARES AND T SNARES
IN A CELL.
THEY'RE SHOWN HERE IN DIFFERENT
COLORS.
THE V SNARE ENCAPSULATED IN THE
VESICLE THAT DEPARTS THE
ENDOPALACE MIC RETICULUM CAN
ONLY MATE WITH COGNATE T SNARE
LOCATED AT THE ENTRY FACE OF THE
GOLGI.
THAT'S ONE OF THE SEVERAL
MOLECULAR FEATURES, NOT THE ONLY
FEATURE BUT A CRITICAL MOLECULAR
FEATURE THAT DICTATES FUSION OF
THIS VESICAL HERE, NOT THERE,
NOT ANY PLACE ELSE AND ALLOWS
SPECIFIC MEMBRANE TRAFFIC IN THE
CELL.
SIMILARLY THERE'S A DIFFERENT
BUT STRUCTURALLY RELATED
HOMOLOGOUS V SNARE PACKAGED TO
VESICALES LEAVING THE EXIT OF
THE GOLGI THAT FINDS ITS PARTNER
IN THE PLASMA MEMBRANE THAT'S A
DIFFERENT V AND T SNARE
DEPENDING WHICH SURFACE OF THE
CELL, APICAL OR BASAL LATERAL.
I COULD GO ON AND ON BUT I
WON'T.
SO THE SPECIFIC PAIRING OF
PROTEINS BETWEEN PARTNERED
MEMBRANES INCLUDING THE RELEASE
OF VESICALES AT THE CELL SURFACE
AS A SPECIAL CASE BUT A VERY
IMPORTANT SPECIAL CASE OCCURS.
ALL THESE PROCESSES ACCEPT
FUSION WITH THE PLASMA MEMBRANE
ARE WHAT CELL BIOLOGISTS CALL
CONSTITUTIVE PROCESS.
THEY OCCUR AL THE TIME.
THEY OCCUR THROUGHOUT THE CELL
CYCLE.
YES, THERE MAYBE REGULATION OF
ONE SORT OR ANOTHER, NO DOUBT
BUT THEY OCCUR ALL THE TIME.
THIS PUTS THEM INTO A
FUNDAMENTAL DISTINCTION WITH
CERTAIN CLASSES OF FUSION WITH
THE PLASMA MEMBRANE, EXOCYTOSIS,
WHICH ONLY OCCUR SOME OF THE
TIME WHEN SIGNAL IS PROVIDED AS
IN THE RELEASE OF
NEUROTRANSMITTER WHEN CALCIUM
ENTERS SECONDARY TO THE ARRIVAL
OF AN ACTION POTENTIAL.
TIME COURSE HERE IS RELATIVELY
LEISURELY FROM THE TIME A
VESICAL DOCKS TO FUSION
TYPICALLY TAKES TEN SECONDS TO A
MINUTE DEPENDING ON THE
SITUATION.
THAT'S THE TIME FRAME.
DIFFERENT THAN THE TIME FRAME IN
SYNAPTIC TRANSMISSION.
WHICH THE NEUROTRANSMITTER CAN
BE RELEASED AS FAST AS 200
MICROSECONDS FROM THE TIMECAL
YUM HAVES.
SO THAT IS THE CONTRA
DISTINCTION HERE.
WHAT CONFOUNDS THIS FURTHER IS
SNARE PROTEINS WHICH I'LL
DESCRIBE IN INCREASINGLY GREATER
DETAIL IN TERMS OF HOW THEY FUSE
BILAYER ARE INTRINSICALLY
POWERFUL FUSION PROTEINS THAT
ARE ON RATHER THAN OFF.
HOW CAN YOU HAVE A
NEUROTRANSMITTER VESICAL SITTING
RIGHT NEXT TO THE PRE-SYNAPTIC
MEMBRANE WITH POTENT FUSION
MACHINERY BY IN AND OF ITSELF IS
ON NOT OFF AND SOMEHOW DOESN'T
FUSE.
BUT THEN BUT THEN AT THE RIGHT
MOMENT IT FUSES RAPIDLY.
SOME ANSWERS BEGIN TO COME FROM
AN UNDERSTANDING OF THE
UNDERLYING PRINCIPLE OF MEMBRANE
FUSION.
ENCAPSULATED BETWEEN THE TWO
STRUCTURES.
THE SNARE PROTEINS ARE ALPHA
HELICAL BUNDLE PROTEIN,
RELATIVELY SMALL, THEY HAVE TWO
PARTS ALL A PART IN THE
MEMBRANE, A TRANSMEMBRANE AND
THEN THEY HAVE A HELIX FORMING
SO CALLED SNARE MOTIF THAT IS IN
THE CYTOPLASM.
THE V?úzBRE EMANATES PRIMARILY
FROM THE VESICAL, THAT'S WHY
IT'S CALLED THE V SNARE FOR
VESICLE AND CONSISTS OF A SINGLE
HELICAL PROTEIN CYTOPALACE MIC
DOMAIN.
THE T SNARE, STANDING FOR TARGET
MEMBRANE VESICLE FUSE WITH THE
PLASMA MEMBRANE, THE T SNARE
CONTRIBUTES THREE HELICES, WHEN
IT ASSEMBLES IT FORMS A FOUR
HELIX BUNDLE THAT FOUR HELIX
BUNDLE IS STABLE SO THAT IF YOU
ISOLATE THIS PROTEIN, THIS
COMPLEX FROM CELLS OR FROM BRAIN
OR FORM IT ARTIFICIALLY WITH
RECOMBINANT PROTEINS, YOU HAVE
TO FIND AND OTHERS FOUND OF
COURSE YOU HAVE TO HEAT THIS
PROTEIN TO ALMOST 100-DEGREES,
YOU HAVE TO BOIL THE WATER FOR
IT TO DENATURE THAT'S HOW STABLE
IT IS.
THERE'S A VERY INTERESTING
FEATURE.
THESE PROTEINS WANT TO FOLD THE
MAKE A FOUR HELIX BUNDLE BUT
THEY CAN'T DO THAT WHEN BETWEEN
TWO BILAYERS.
IT'S FROM THIS THE PRINCIPLE OF
FUSION FOLLOWS.
THE V SNARE UNIQUELY ASSEMBLING
FROM SYNAPTIC VESICAL.
THE T SNARE IS ASSEMBLING FROM
THE MAMA MEMBRANE.
AS THESE TWO ZIPPER UP FROM
MEMBRANE DISTAL END TERMINI
TOWARDS THE MEMBRANE, THEY CAN
ASSEMBLE BUT THEY CAN'T
COMPLETELY ASSEMBLE.
I HOPE EVERYBODY CAN SEE THAT.
LEFT TO THEIR OWN DEVICES,
REMOVED FROM MEMBRANE ENTIRELY,
THEY DO FULL WILL ASSEMBLE.
EVEN THE TRANS MEMBRANES FIND
EACH OTHER.
SO THEY WANT TO ZIPPER UP TO
THIS TIGHT FOUR HELIX BOPPED L
BUT THEY CAN'T.
WHY CAN'T THEY?
THEY TWO BILAYERS ARE SEPARATE.
THE ONLY WAY THESE TWO BILAYERS
BECOME ONE BILAYER CAN THE THEY
ZIPPER.
SO WHAT WE HAVE HERE IS
THERMODYNAMIC LINKAGE DUE TOSER
UK EXCLUSION OF TWO REACTIONS,
THE FIRST REACTION IS A PROTEIN
FOLDING REACTION.
THE V SNARE ESPECIALLY IS A
REASON DOCUMENT COIL AND THE T
SNARE WITH THREE SUBUNITS IS
LOOSELY AABLED BEFORE IT
EPICOUNTERS THE V SNARE.
IN THIS STATE THE SNARES ARE
PARTIALLY OR COMPLETELY
UNFOLDED.
IN THIS STATE AFTER FUSION IN
GOING FROM UNFOLDED TO
COMPLETELY FOLDED THERE'S A LOT
OF ENERGY POTENTIALLY RELEASED.
IF IT'S MIXED IN A DETERGENT
SOLUTION OR WATER, THEY WILL
GIVE THAT ENERGY OFF AS HEAT.
PLACED BETWEEN TWO BILAYERS IF
-- IT'S -- THEY WILL PROVIDE
ENOUGH ENERGY TO DO WORK ON THE
BILAYER TO CAUSE THE BILAYERS TO
FUSE.
OBVIOUSLY WE DON'TNESS EVERY
DETAIL ABOUT THAT TRANSMISSION
AND THERE'S A LOT OF IMPORTANT
WORK GOING ON, NOT THE LEAST
FROM JOSH ZIMMERBURG AND OTHERS
HERE.
AND THERE ARE A NUMBER OF
COMPETING MODELS BUT WHAT IS
CLEAR IS THE ASSEMBLY OF SNARES
CREATES AN INNER FORCE THAT PULL
IT IS MEMBRANES TOGETHER AND
THAT FORCE RESULTS IN OPENING OF
A FUSION PORE TO RELEASE THE
NEUROTRANSMITTER OR SOME
EQUIVALENT CARGO.
WE KNOW THIS OCCURS WITH
ISOLATED SNARE PROTEINS.
THE TIME COURSE IS MEASUREED IN
A NUMBER OF LABORATORIES, IT'S
LESS THAN 100 MILLISECONDS, IT'S
TYPICALLY MORE THE AVERAGE
MEASUREMENT IS PROBABLY 30 TO 50
MILLISECONDS.
IF YOU HAVE ISOLATED PROTEINS
WITH A V SNARE BILAYER THAT'S
THE TIME COURSE THE SNARES WILL
FUSE.
THEY ARE EXTREMELY COMPETENT.
RECENT STUDIES FROM
(INDISCERNIBLE) LAB AND WE
CONFIRMED THIS SHOW THAT A
SINGLE SNARE COMPLEX THAT'S
ASSEMBLING WE CALL IT A SNARE
PIN, WILL BE SUFFICIENT AT LEAST
AT A CERTAIN RATE ENERGETICALLY
SUFFICIENT TO DRIVE THE FUSION
OF A VESICLE WITH A BILAYER.
THESE ARE ENERGETICALLY
COMPETENT.
SO WE HAVE MEASURED THIS INNER
DIRECTED FORCE DIRECTLY USING
THE SURFACE FORCE APPARATUS
WHERE WE HAVE SNARES IN OPPOSITE
MEMBRANES BRING TOGETHER WITH
SUB-NANOMETER POSITION, PULL
THEM APPEARED IN A DEFINED WAY
AND MEASURE ADHESIVE FORCE.
IT IS A FORCE AND ENERGY
PERFECTLY CONSISTENT WITH THE
IDEA THAT A SINGLE SNARE PIN IS
ENERGETICALLY CAPABLE OF FUSING
A LIPID BILAYER.
FINALLY IN CASE SOMEONE ASKS AT
THE END OF THIS FUSION PROCESS
THERE'S AN ENZYME SYSTEM
INVOLVING THE TRIPLE AATPASE
CALLED NSF THAT UTILIZE A TP
HYDROLYSIS TO SEPARATE SNARES
UNFOLD AND ALLOW TO BE RECYCLED
ENERGETICALLY TO THE HIGH ENERGY
STATE OF UNFOLDED PROTEIN AND P
TO INITIATE RECYCLING TO THE
CORRECT DONOR COMPARTMENT.
THIS IS OUR CURRENT
UNDERSTANDING IN CARTOON LEVEL
ANYWAY HOW MEMBRANE FUSION
WORKS.
TO MAKE IT MORE CONCRETE I'LL
DRAW UPON A RECENT X-RAY CRYSTAL
STRUCTURE OF RYAN HART AND
COLLEAGUES, THAT SHOWS THE FOUR
HELIC BUNDLE.
THIS IS OF THE SYNAPTIC SNARE
PROTEIN.
BY WHICH OF INTRODUCTION THESE
ARE THE PROTEINS THAT DO THE JOB
TO RELEASE NEUROTRANSMITTER AT
SYNAPSES.
THE V SNARE CONSISTS OF A
PROTEIN CALLED VAMP OR
SYNAPTOBREVIN AND IT ORIGINATES
IN THE SYNAPTIC VESICAL.
THE T SNARE CONSISTS OF TWO
PROTEIN, INTEGRAL MEMBRANE
PROTEIN CALLED SYNTAXIN, AND
SOLUBLE PROTEIN CALLED SNAP 25
WHICH CONTRIBUTES TWO OF THE
HELICES.
SO THE T SNARE HERE CONSISTS OF
THREE HELICES, TWO CONTRIBUTED
BY SNAP 25 IN GREEN, ONE
CONTRIBUTED BY MEMBRANE PROTEIN
SEN TAX AND PLASMA MEMBRANE
INITIALLY AND THE OTHER THE
VESICLE PROTEIN VAMP INITIALLY
IN THE SYNAPTIC( VESICAL.
I WANT TO DISTINGUISH THREE
REGIONS, THERE IS A REGION
CALLED THE BUNDLE REGION OR THE
HELICAL BUNDLE REGION YOU CAN
SEE IT'S CALLED THAT FOR OBVIOUS
REASONS.
SNAP 25 TERMINATES AT THAT POINT
AND VAMP AND SYNTAX AND CONTINUE
TO INTERACT IN A REGION CALLED
THE LINKER REGION WHICH DOES NOT
INCLUDE CONTRIBUTIONS FROM SNAP
25, THE LINKER BECAUSE IT
CONNECTS THE FOUR HELIX BUNDLE
TO THE MEMBRANE AND THEN YOU
HAVE THE TRANSMEMBRANE DOMAIN OF
V SNARE AND T SNARE.
VAMP AND SYNTAXIN.
THIS IS THE POST FUSION STATE
THAT EXISTS AFTER THE FUSION.
IF WE WANT TO UNDERSTAND THE
MECHANISM OF FUSION MORE WE NEED
TO UNDERSTAND FOR ABOUT
STRUCTURE AS ASSEMBLING RATHER
THAN AFTER ASYSTEMBLY BUT THIS
PROVIDES OOH VERY IMPORTANT
GUIDE.
IMPORTANT LIT IT SHOWED SCRATCH
AND SYNTAXIN CONTINUE THE
INTERACT WITH A SERIES OF
CONTACTS INTO THE BILAYER, EVEN
AFTER FUSION.
THIS ZIPPERING PROCESS EVIDENTLY
PROCEEDS RIGHT THE WAY THROUGH
THE FUSION PROCESS.
NOW, IF I DIDN'T GET ANYTHING
ACROSS HERE, I WOULD LIKE TO
TAKE A MOMENT AND SUMMARIZE 25
YEARS OF MY LIFE IN THIS ONE
SLIDE WHICH EXPLAINS HOW I THINK
ABOUT THE PROBLEM.
I HOPE NOBODY IS OFFENDED.
THIS IS A READY'S HAIR PIN.
ANY OF YOU WHO HAVE HAD THE
EXPERIENCE OF TRYING TO SEPARATE
THE TWO ENDS OF A LADY HAIR PIN
WILL KNOW THAT IT TAKES WORK TO
DO THAT.
SO LET'S IMAGINE THIS IS A SNARE
PIN ASSEMBLING BETWEEN TWO
VESICALES EXPECT E START WHEN
IT'S ASSEMBLED, NOW WE PULLED IT
APART.
HAVING PULLED IT APART, WE'RE
GOING TO INSERT EACH END INTO A
RUBBER BALL REPRESENTING TWO
VESICALES OR IF YOU WILL, A
SYNAPTIC VESICAL AND PLASMA
MEMBRANE.
NOW WHAT WE'RE GOING TO DO IS
LET THEM GO.
AS WE LET THIS GO WHAT HAPPENS?
THE PIN BECAUSE IT WAS RESTORING
FORCE INWARD DIRECTED FORCE
THAT'S THE FORCE I'M REFERRING
TO THAT OCCURS BETWEEN SNARE
PINS.
IT WILL -- WHAT WILL THIS PIN
DO?
IT WILL FORCE TOGETHER TWO
RUBBER BALLS.
THAT'S THE END OF IT IF IT'S
RUBBER BALLS BUT IF THEY'RE NOT
THEY HAVE A LIQUID LIKE
CHARACTER WHICH IN PHICAL TERMS
MEANS THEY HAVE SURFACE TENSION
THAT CAN BE OVERCOME EXERTED BY
THE PIN, THE SNARE PIN IN
REALITY, THEN THE TWO BALLS WILL
BE BLENDED INTO ONE WHICH ALLOWS
THE PIN TO REACH ITS BROWN STATE
AND P ITS MINIMUM ENERGY STATE.
IN MY VIEW TRAINLY FUSION IS
NOTHING MORE OR ANYTHING LESS
THAN THIS.
THERE ARE A LOT OF DEBATES ABOUT
THE TRANSITION STATE WHEN THOSE
TWO BALLS ARE ABOUT TO GO
TOGETHER.
AND I TEND TO LOOK AT THAT AS A
STATISTICAL MECHANICAL DEBATE OF
INTEREST.
FROM A BIOLOGICAL POINT OF VIEW
HOWEVER, OF GREATER INTEREST IS
THE THERM MOW DYNAMICS THAT A
PRE-CONDITION IS CREATED THAT
MAKES THE FUSION INEVITABLE.
THIS EXAMPLE IS NOT AN IDOL ONE,
IN RECENT MONTHS MY COLLEAGUES
GRABBED OUR HANDS ON INDIVIDUAL
SNARED COMPLEXES AN LITERALLY
PRIED THEM APART WITH OPTICAL
TWEEZERS.
SO HERE WHAT A COLLEAGUE IN CELL
BIOLOGY IN HIS LAB AND WHAT WE
HAVE DONE IS TO ATTACH A SMALL
BEAD BY MOLECULAR MODIFICATION
TO THE ASSEMBLED END OF A SNARE
COMPLEX.
WE ARTIFICIALLY CROSS LINK THE V
AN T SNARE, THE SAME SNARES YOU
SAW A MOMENT AGO, AND WE
ARTIFICIALLY CONNECTED THEM AT
THEIR MEMBRANE DISTAL END
TERMINI.
THE ATTACHMENTS WOULD BE HERE.
THE ANCHORS ARE REMOVED AND
REPLACED BY A LINKER TO ONE BEAD
AND LINKER TO THE OTHER ON VAMP
AND SYNTAXIN.
NOW WHAT WE CAN DO WHAT I
ILLUSTRATED A MOMENT AGOND PULL
ON THEM IN A DETERMINED WAY.
WHAT WE OBSERVE IS AS WE DO THEY
MELT LAYER BY LAYER.
THE FIRST THING THAT MELTS IS
THE LINKER LAYER.
THE SECOND THING THAT MELTS IS
HALF OF THE FOUR HELIX BOPPED L.
AND NULL REVERSIBLY SO AS YOU
PULL YOU GET WHAT A SINGLE
CHANNEL FIZZ IDEAL GIST WOULD
RECOGNIZE A SINGLE CHANNEL
BEHAVIOR.
BECAUSE THE LINKER HAS BEEN
DESTABILIZED AND CERTAIN FORCE
LEVELgÑ" FLUCTUATES BETWEEN OPEN
CLOSED, OPEN CLOSED.
AS IT OPENS THE DISTANCE BETWEEN
THE TWO BEADS INCREASES AND
THAT'S WHAT WE'RE MEASURING
HERE.
THIS WILL GO ON FOREVER UNLESS
WE EXERT MORE FORCE AND WE GET
TO THE NEXT FORCE LEVEL WE GO TO
THE NEXT PORTION WHICH
FLUCTUATES BECOME AND FORTH.
ONE BEAUTY OF THIS EXPERIMENT
BESIDES DEMONSTRATING THE BINARY
LIKE SWITCH NATURE OF DOMAINS IS
IT ALLOWS US TO MEASURE KINETICS
WITH WHICH THIS FLIPPING BACK
AND FORTH OCCURS.
REMARKABLY ENOUGH FOR THE
SYNAPTIC SNARE COMPLEX THE RATE
OF REZIPPERRING HERE OCCURS WHAT
WE ESTIMATE TO BE A DEIFYING
CONTROLLED LIMIT.
-- DIFFUSION CONTROLLED LIMIT.
AS FAST AS THE V SNARE ZIPPERS
IN AND P LAYS DOWN, BY
DISPLACING WATER, THAT'S HOW
FAST IT MOVES.
THIS MACHINE IS NOT ONLY NEE
JETTICLY SUFFICIENT FOR FUSION
BUT -- ENERGETICALLY FOR FUSION
BUT DESIGNED AS FAST AS PHYSICS
ALLOW WHICH IS A WONDERFUL FACT
WHEN WE CONSIDER HOW FAST
SYNAPTIC VESICLE RELEASE HAS TO
OCCUR, THE TWO HUNDRED
MICROSECONDS.
I WANTED YOU TO KNOW THAT THERE
IS A PAUSE IN THE DISASSEMBLY.
WE BUST THIS PART, BUST THAT
PART AND IF WE PULL HARDER WHICH
IS NOT SHOWN HERE WE PULL THE
LAST PART CALLED THE END
TERMINAL DOMAIN, LINKER DOMAIN,
END TERMINAL DOMAIN IS LAST,
THERE'S THE GUY THAT ASSEMBLES
FIRST WHEN THE VESICAL STARTS
DOCKING.
THAT TURNS OUT TO BE VERY, VERY
SLOW.
IT'S VERY SLOW, MEASURED
ACTUALLY RATE CONSTANT IS
MEASURED ON THE ORDER OF AN
HOUR.
THE REASON IT'S SO SLOW IS BY
BEING SO SLOW IT ALLOWS OTHER
FACTORS TO KICK IN THAT CAN
REGULATE THE DOCKING OF THE
VESICAL.
SO YOU HAVE FACTORS UPSTREAM AND
YOU'LL SEE THAT REGULATE DOCKING
OF THE VESICAL TO ALLOW IT TO
ZIPPER THROUGH THE END TERMINAL
DOMAIN.
I'LL GIVE THE STORY AWAY NOW
BECAUSE YOU'LL SEE THAT IN THE
SPECIAL CASE OF THE SYNAPTIC
VESICAL, THE VESICAL IS FROZEN
AT THIS STAGE.
HALFWAY ZIPPERED PUNT WAITED BY
-- ONCE WAITED BY IONIC LAYER,
THESE ARE HOPE TAB REPEATS, AND
THOSE A CERTAIN IN EVERY SNARE
COMPLEX IS REPLACED BY
HYDROPHYLIC RESIDUE.
THIS CAUSES AN INTENTIONAL PAUSE
HALFWAY THROUGH THE ZIPPERING
PROCESS.
AND IN THE SYNAPSE THERE ARE
OTHER PROTEINS AND I WILL
DESCRIBE THEM TO YOU, THAT GRAB
THE SNARE COMPLEX QUITE
LITERALLY, AT THIS PAUSE POINT
AND FREES IT UNTIL THE ACTION
POTENTIAL ARRIVES, UNTIL CALCIUM
ARRIVES.
AND THAT IS REALLY NIFTY BECAUSE
IT ALLOWS THE SNARE COMPLEX TO
BE ACTIVATED FROM A VESICAL
WHOSE FRAME IS FROZEN JUST
BEFORE MEMBRANE FUSION CAN BE
COMPLETED AT A DIFFUSION
CONTROLLED LIMIT.
THAT IS OUR PICTURE OF HOW THIS
WORKS.
TO SUMMARIZE THEN, THERE IS IN
THE ASSEMBLED SNARE COMPLEX
DISCREET DOMAINS, END TERMINAL,
C TERMINAL DOMAIN, AND
TRANSMEMBRANE DOMAIN.
THEY HAVE DISTINCT FUNCTIONS.
THE PURPOSE OF THE THE END
TERMINAL DOMAIN WHICH ASSEMBLES
FIRST IS TO DOCK THE VESICAL
TIGHTLY TO THE PLASMA MEMBRANE.
THE NEXT ASSEMBLY OF THE C
TERMINAL DOMAIN IRREVOCABLY
COMMITS THE VESICLE TO FUSE.
THE ACTUAL FUSION OCCURS AS BEST
WE CAN JUDGE SUMMARIZING WORK
FROM MY LAB AND RYANHART YAN'S
LAB HERE WHEN LINKER DOMAIN
ASSEMBLABLES.
THEN THE TRANSMEMBRANE DOMAIN IS
BELIEVE TO HAVE ASSEMBLED BY THE
X-RAY CRYSTALOGRAPHY.
SINCE THE FUSION OF THE BILAYERS
MEASURED BY ZIPPERING --
TRIGGERED BY LINKER DOMAIN
ZIPPERING AND THE MIXING OF THE
LIPID BILAYER AND THE INITIAL
OPENING OF THE FUSION PORE, ALL
THIS WOULD SEEM TO BE OVER SO IT
WOULD SEEM TO BE NO ROLE
NECESSARILY FOR THE ZIPPERING OF
THE TRANSMEMBRANE DOMAIN BUT
ACTUALLY NOTHING COULD BE
FURTHER FROM THE TRUTH BECAUSE
AS WE RECENTLY PUBLISHED, THE
ZIPPERING OF THE TRANSMEMBRANE
DOMAIN AFTER FUSION HAS
OCCURRED, AFTER THE FUSION PORE
JUST OPENS SEEMS CRITICAL BASED
ON IN VITRO EMPERIMENTS FOR THE
OPENING OF THE FUSION PORE,
EXPANSION OF THE FUSION PORE.
I WON'T REALLY HAVE TIME TO GO
INTO THIS IN DETAIL BUT IF
YOU'RE INTERESTED THIS WAS VERY
REISN'TLY PUBLISHED IN SCIENCE,
LAY SHI IS THE PERSON WITH THE
MOST WORK ON THIS IN THE LAB.
IT INVOLVES A NOVEL ASSAY IN
WHICH WE MEASURE THE FUSION OF
SNARE CONTAINING ARTIFICIAL
VESICALES WITH V SNARE CON
TAPING VESICALES WITH T SNARE
CONTAINING NANODISC.
IT OPENS A HOLE DURING THE
FUSION PROCESS SO WE CAN MEASURE
RELEASE OF CONTENT AS A PROXY
FOR THE OPENING OF A FUSION
PORE.
WE ON SERVE IN NO INSTANCE IS
THERE A BIG DIFFERENCE, YOU GET
LIPID MIXING WITH OR WITHOUT THE
VARIOUS MUTATIONS I DESCRIBE BUT
GOING TO RYAN HART'S STRUCTURE
WHEN WE MUTATE KNOWN CONTACTS IN
HIS CRYSTAL STRUCTURE BETWEEN
THE VAMP AND SYNTAXIN
TRANSMEMBRANE ANCHORS WE GET
SLOW OPENING OF THE FUSION PORE
THOUGH FUSION OCCURRED WITH THE
NORMAL SPEED.
THE LINKER DOMAINS ARE INTACT,
THE BILAYERS ARE FUSED.
YOU CAN'T HAVE TOP LOGICAL
FUSION WITHOUT SOME OPENING OF
THE FUSION PORE SO YOU GET SOME
RELEASE BUT THE RATE OF RELEASE
IS DRASTICALLY INCREASED.
IF YOU MUTATE THE NON-CONTACT
RESIDUES WE'RE SHOWING ONLY A
COUPLE HERE BUT WE HAVE DONE IT
EXHAUSTIVELY, EVERY MOLECULAR
CONTACT OBSERVED HERE IS
IMPORTANT FOR OPENING OF THE
FUSION PORE.
SO WE'RE NOW TURNING TO
PHYSIOLOGICAL SYSTEMS TO SEE IF
THIS IS PHYSIOLOGICALLY RELEVANT
BUT CERTAINLY SUGGESTS THAT EACH
DOMAIN OF THE SNARE COMPLEXIN
COLLUDING THE TRANSMEMBRANE HAS
A CRITICAL ROLE.
SO NOW I WOULD LIKE TO
ENCAPSULATE THIS IN ONE MORE
VIDEO.
SO HERE WE HAVE
NEUROTRANSMITTERS STORED IN A
SYNAPTIC VESICAL.
AND THE REASON I WOULD LIKE TO
SHOW YOU THIS THOUGH IT'S PREPPY
SHUTS, IT WILL OR YEN YOU TO
WHAT'S NEXT WHICH IS A LITTLE
MORE DIFFICULT.
SO HERE WHAT WE HAVE IS THE T
SNARE IN THE PLASMA MEMBRANE AND
IN THE INITIAL STEP -- STATE
WHERE THE VESICAL IS DOCKED THE
END TERMINAL PORTION OF THE V
SNARE VAMP IS HELIX.
IT'S HELICAL STATE HALF ZIPPERED
THROUGH THE HELICAL BUNDLE SO TO
SPEAK HALFWAY FORMED.
BUT THE REMAINDER OF THE V SNARE
INCLUDING C TERMINAL HALF THAT
WILL FORM THE BUNDLE AND LINKER
PORTION HAS NOT YET ZIPPERED.
WE BELIEVE FOR REASONS YOU'LL
SEE THAT THAT IS THE POINT AT
WHICH SYNAPTIC TRANSMISSION IS
PAUSED TO ALLOW SIN CROW IN
THISTY.
SIN CROW IN THISTY RESULTS
BECAUSE THE -- SIN CROW IN
THISTY RESULTS BECAUSE IT IS
ACCUMULATED AND THEREFORE BEEN
RELEASED SYNCHRONOUSLY.
IF THEY'RE IN THE ACCUMULATED AT
A DEFINED STAGE THEY CANNOT BE
RELEASED SYNCHRONOUSLY.
IT'S FUNDAMENTAL TO THE PROCESS.
NEXT THING THIS IS IN THE
ABSENCE OF REGULATION, THE
GENERAL FUSION PROCESS AS WE
UNDERSTAND IT, IS THAT THE C
TERMINAL PORTION OF THE VAMP
ZIPPERS, THIS IS WHAT COMMIT TO
FUSION.
THEN THE LINKER ZIPPERS, AS THE
ZIPPERS OPENS UP THE FUSION PORE
INITIALLY BUT ONLY SO FAR.
THEN FINALLY AS THE
TRANSMEMBRANE ZIPPER, THIS
DRIVES WE THINK IT PRODUCES A
RADIAL FORCE SO WE DON'T REALLY
KNOW THIS, IT'S SPECULATION,
LITERALLY FORCE IT IS FUSION
PORE OPEN.
THAT'S OUR VIEW OF MEMBRANE
FUSION FROM THE POINT OF VIEW OF
THE PROTEINS.
NOW I WILL LIKE TO COME BACK
WITH BACKGROUND TO THE VERY
SPECIFIC PROBLEM, HERE YOU HAVE
A VESICLE, IT HAS IN VIVO A MUCH
HIGHER CONCENTRATION OF V SNARES
THAN ANY IN VITRO SYSTEMS.
WE MIGHT TYPICALLY WORK WITH
FIVE, TEN VAMPS IN AN ARTIFICIAL
VESICAL OF THIS SIZE IN VITRO.
BUT THE V SNARE HERE WAS PRESENT
AT 70 COPIES PER VESICAL.
THE T SNARE SYNTAXIN IS PRESENT
AT PERHAPS ONE COPY FOR EVERY
THOUSAND PHOSPHOLIPID MOLECULES
IN THE ARTIFICIAL BILAYERS WE
USE.
HERE IT'S PRESENT IN CLUSTERS
THAT ARE ALMOST PURE WITH
RESPECT TO SYNTAXICSN ACCORDING
TO THE LATEST WORK.
REMARKABLY ENOUGH THESE
VESICALES STAY WHERE THEY ARE,
THEY DON'T FUSE, EVEN THOUGH IF
YOU TAKE SAME PROTEINS OUT OF
THE SYNAPSE, YOU PUT THEM INTO
BILAYERS AT LOWER
CONCENTRATIONS, WITHIN 50, 100
MILISECONDS THEY HAVE FUSED.
I HAPPEN TO BE A BELIEVER IN
PHYSICS.
I HAPPEN TO BELIEVE THAT PHYSICS
DOESN'T DISAPPEAR WHEN YOU BUT
MOLECULES TO A CELL.
THE BIOPHYSICS REPRESENTS THE
GROUND TROOP OF WHAT A PROTEIN
CAN DO.
THAT GROUND TROOP DOESN'T CHANGE
WHEN PROTEINS ARE PLACED IN THE
CELL.
I HAVE TO CONCLUDE FROM THIS
THAT THERE'S A CLAMP THAT LOCKS
THE EXOCYTOSIS PROCESS AND
BLOCKS ABOUT 50 -- BLOCKS IT
PROBABLY ABOUT A MILLISECOND OR
LESS BEFORE THE RELEASE PROCESS.
WHAT IS THAT CLAMP?
OVER A TEN YEAR PERIOD WE TRIED
TO FIND OUT WHAT THAT CLAMP WAS.
IN ABOUT 2005 WE DISCOVERED WHAT
IT WAS.
WAS A PROTEIN DISCOVERED BY TOM
PSEUDOOFT CALLED COMPLEXIN, AS
THE NAME SUGGESTS IT'S A COMPLEX
PROTEIN.
SOMETIMES NAMES NEVER FALL EWE
EVEN IF TERRIBLE NAMES.
IT WAS COMPLEXIN BECAUSE IT
FORMED A COMPLEX WITH A SNARE
MENTION AND NOBODY ELSE KNEW
WHAT IT IS AT THE TIME IT WAS
NEEDED FOR SYNAPTIC
NEUROTRANSMITTER RELEASE, WE
WON'T HAVE TIME TO GO INTO THIS,
IT HAS POSITIVE ROLES AN
NEGATIVE ROLES, IT IS BOTH AN
ACTIVATOR AND INHIBITOR.
BUT MOST IMPORTANTLY I WOULD
LIKE TO CONCENTRATE ON ITS ROLE
AS CLAMP OR INHIBITOR.
WHICH WE FOUND WHEN WE ADDEDDED
COMPLEXIN AS A CANDIDATE CLAMP
TO FUSION SYSTEMS THAT CONTAIN
DEFINED VAMP SYNTAXIN SNAP 25,
THAT OTHERWISE FUSED.
IF YOU ADD COMPLEXIN AT HIGH
ENOUGH CONCENTRATION THEY DIDN'T
FUSE.
WITH THAT THAT MEAN?
NOT NECESSARILY ANYTHING BUT IF
WE ADD CALCIUM SENSOR BACK AND
ONLY THEN IF WE ADD CALCIUM
COULD WE RESTORE FUSION IN THIS
ARTIFICIAL SYSTEM.
THAT SUGGESTED THATN%" PLEXIN COULD
BE THE CLAMP.
TOM PSEUDOOFF AND OTHERS SINCE
HAVE MUCH MOVE PHYSIOLOGICAL
EMPERIMENTS THAT SHOW THIS
BEYOND A DOUBT AND I'LL SHOW YOU
A COUPLE SUCH EXPERIMENTS TODAY.
TOM AND JOSEPH SOLVED THE X-RAY
LISTAL STRUCTURE OF COMPLEXIN IN
THE EARLY 2000s, THE HELICAL
PROTEIN THEY ARE PROBABLY THE
ONE THING YOU NEED TO KNOW ABOUT
IN THIS ENTIRE FIELD.
IN VESICAL TRAFFICKING IT'S
MOSTLY ABOUT HELICES INCLUDING
TETHER PROTEINS.
COMPLEXIN BINDS TO THE OUTSIDE
OF THIS HELIC BUN L AND THE
MEMBRANE PROXIMAL HALF.
IMPORTANTLY THIS IS THE
STRUCTURE OF COMPLEXIN WHEN IT
IS BOUND TO THE FULLY ASSEMBLED
COMPLEX WHICH ONLY OCCURS AFTER
FUSION IT DOES NOT NECESSARILY
INFORM US THEREFORE ABOUT THE
ROLE THAT COMPLEXIN PLAYS DURING
THE FUSION PROCESS.
WHERE IT ACTS AS A CLAMP.
WE ADDED COMPLEXIN TO THE
SURFACE FORCE APPARATUS
EXPERIMENT, A PIVOTAL EXPERIMENT
HERE, FRED PALSA AND I AND HIS
LABORATORY IN PARIS,
(INDISCERNIBLE) WE FOUND
COMPLEXIN CREATE AS NEW STATE
WHICH THE SNARE COMPLEXES FROZEN
IN THE HALF ZIPPERED STATE, 50%
AS BEST WE CAN.
SO WE KNEW IT DID SOMETHING
IMPORTANT AND IT SOMEHOW COULD
BE THE CLAMP.
SO THE NEXT QUESTION WAS HOW
DOES COMPLEXIN CLAMP?
AS I WARNED YOU, I'M GOING TO
ILLUSTRATE THIS BY A MODEL AND
THEN SHOW YOU THE X-RAY CRYSTAL
WORK IN THE CONTROLS, THAT STAND
BEHIND IT.
OUR PRESENT UNDERSTANDING ARE
REACHED BY KAREN RYANSH AN X-RAY
CRYSTALOGRAPHER DEPARTMENT OF
YALE IN MY LABORATORY SHOWN
HERE.
THIS IS THE HALF ASSEMBLED SNARE
COMPLEX WHERE THE INTERVENTION
BY COMPLEXIN WE BELIEVE BEGINS.
THE COMPLEXIN HELIX ACTUAL HI
HAS TWO PARTS.
THE CENTRAL HELIX AND THE
ACCESSORY HELIC.
THE CENTRAL HELIX IS ENDOWED
WITH THE ABILITY TO BIND VAMP
AND SYNTAXIN AND BINDS TO THE
ASSEMBLED SNARE PIN.
IN FACT, IT BINDS TO PORTIONS
THAT ARE PRESENT BUT ONLY
PRESENT WHEN THE SNARE COMPLEX
IS HALF ZIPPERED.
SO BEFORE THIS STATE, THERE'S NO
BINDING BY COMPLEXIN.
WHEN VN AS WE CALL IT IS HALF
ZIPPERED TO THE IONIC LAYER THAT
I MENTIONED, THEN THE BINDING
SITE IS CREATED FOR THE CENTRAL
HELIX.
WHEN THAT HAPPENS, THE COMPLEXIN
BINDS.
IT BINDS IN SUCH A WAY TO LEAVE
THE ACCESSORY HELIX POINTING
OUT.
THE CENTRAL HELIC BINDING TO THE
SNARE COMPLEX IS VERY IMPORTANT.
BECAUSE IT MEANS THAT YOU WILL
ALWAYS HAVE A COMPLEXIN THERE.
BY THE WAY, REMEMBER I MENTIONED
THAT THIS INITIAL BINDING OF VN
TO THE T SNARE IS VERY, VERY
SLOW.
ONE OF THE FACTORS THAT
DRASTICALLY ACCELERATES IT IS
THE ACCESSORY HELIC.
SO THIS DESIGN ENSURES THAT THE
ACCESSORY HELIC THE COMPLEXIN
THE LOADED AT THE TIME THE
VESICAL FIRMLY DOCKS.
SO YOU ARE POSITIONING YOUR
CLAMP IN ORDER TO MAKE SURE
PRE-POSITIONING TO MAKE SURE
IT'S THERE AT THE RIGHT TIME.
THE ACCESSORY HELIX IN FACT WILL
BE DOING THE CLAMPING.
IF OUTTAKE IT OFF, SOME
EXAMPLES, YOU DON'T GET
CLAMPING.
IF YOU MUTATE YOU DON'T GET
CLAMPING.
YOU NEED ACCESSORY HELIX FOR
CLAMPING.
YOU ONLY NEED THE CENTRAL HELIX
FOR THE ACTIVATION OF
NEUROTRANSMITTER RELEASE.
THE NEXT THING THAT HAPPENS IS
THAT THE ACCESSORY HELIX DOES
ITS JOB BY REACHING ACROSS AND
GRABBING A SECOND SNARE PIN.
SO IT CLAMPS IN TRANS.
IN THIS WAY ONE SNARE PIN THAT'S
ASSEMBLED CLAMPS ANOTHER,
MUTUALLY INHIBITING EACH OTHER.
LET'S LOOK AT THIS FROM THE TOP
VIEW IN WHICH WE NOW LOOK AT THE
PROTEINS LYING LIKE A SANDWICH
BETWEEN THE PLASMA MEMBRANE
BELOW AND SYNAPTIC VESICLE
ABOVE.
THE FIRST THING THAT HAPPENS IS
COMPLEXIN BIND BY CENTRAL HELIX.
LEAVING ACCESSORY HELICES FREE
TO BEHIND BETWEEN COMPLEXES.
THE SEQUENCE OF THE ACCESSORY
HELIX IS HOMOLOGOUS TO THE
SEQUENCE OF THE V SNARE IN THE
SAME REGION.
WHICH IS VERY ELEGANT.
'S AN HONNARY V SNARE.
IT GOES RIGHT IN HERE AND BINDS
THE T SNARE A IF IT WERE A V
SNARE BUT P IT'S NOT.
BY BINDING THERE ITW
V SNARE FROM FURTHER ASSEMBLING.
THAT UNFOLDED PORTION OF THE V
SNARE CANNOT CONVERT TO A COIL
BECAUSE TO DO SO IT NEEDS TO
DISPLACE THE COMPLEXICSN.
SO THERE'S A TUG OF CAR
RESULTING IN CLAMPING SO IF THE
ACCESSORY COMPLEXIN HELIX IS
REMOVED AS ILLUSTRATED HERE THE
BLOCK ZIPPERING IS REMOVED AND
FUSION WILL PROCEED.
BUT THAT DOESN'T OCCUR BECAUSE
THE ACCESSORY HELIX IS CLAMPING,
THIS CLAMPING OCCURRING BETWEEN
TWO SNARE PINS.
AS YOU CAN IMAGINE THIS
ACCESSORY HELIX, THERE'S NOTHING
TO PREVENT IT FROM FORMING, FROM
RECRUITING ANOTHER SNARE PIN.
AND ANOTHER ONE TO GIVE RISE TO
WHETHER WE CALL A ZIG ZAG ARRAY
OF -- WHICH IS A HIGHLY
COOPERATIVE STRUCTURE AND THAT
GIVES RISE WE BELIEVE TO SIN
CHRONICITY.
ACCORDING FADING A LARGE NUMBER
OF SNARES IN ONE STRUCTURE THAT
IS ALL OR NONE T HAS THE ALL OR
NONE QUALITY OF COOPERATIVE
STRUCTURE, IT ALL WILL COME
APART AT ONCE, THERE'S A CLEAR
PREDICTION FROM THE STRUCTURE
AND THIS WILL LEAD TO THE
SYNCHRONOUS RELEASE OF A
VESICLE.
SO WE THINK THAT ULTIMATELY IS
WHAT SIN CHRONICITY COMES FROM.
THIS IS HOW WE REGARD CLASPING
TO OCCUR.
HOW DOES ACTIVATION éñ OCCUR?
NOW WHAT WE HAVE GOTTEN TO IS A
CLAMPED VESICAL THAT NEEDS TO BE
RELEASED WHEN CALCIUM ENTERS.
CALCIUM WHEN CALCIUM ENTERS THE
SENSOR FOR CALCIUM IS THE
PROTEIN SYNAPTIC TAGUMEN
DISCOVER AS A VESICAL COMPONENT
BY TOM SUDHOFF.
IN YEARS OF PAINSTAKING WORK
MUCH CONTROVERSIAL BUT NOW WIDE
UNDERSTOOD TO BE CORRECT TOM
WENT TO SHOW IT IS INTACT THE
CALCIUM SENSOR FOR SYNCHRONOUS
NEUROTRANSMITTER RELEASE.
AND PROBABLY THE MOST PERSUASIVE
EXPERIMENT IS A STRUCTURE
ACTIVITY EMPERIMENT WHERE HE
MUTATED THE CALCIUM BINDING
SITES IN SYNAPTOTAGMIN TO
RATCHET CALCIUM BINDING UP OR
DOWN IN TERMS OF BINDING
CONSTANT, PUT IT INTO A MOUSE IN
PLACE OF NORMAL SYNAPTOTAGMIN
GENE AND RATCHET UPPER DOWN
SENSITIVITY AT SYNAPSES
ACCORDINGLY.
SO THAT DOESN'T TELL US HOW
CALCIUM FUSION OCCURS BUT IT
TELLS US IT DOES OCCUR BY MEANS
OF THIS MOLECULE.
SO HOW DOES SYNAPTIC --
SYNAPTOTAGMIN SENSE CALCIUM?
I'M MOVING FROM WHAT I REGARD AS
FACT TO SPECULATION.
ONE THING THAT IS A FACT, THOUGH
IS SYNAPTOTAGMIN IS A TIGHT
BINDER OF MEMBRANES, IT HAS AN
ALOETHATIC LOOP THAT INSERTS TO
THE BILAYER AND INSERTS WHEN
CALCIUM IS BOUND AT THE BINDING
SITES.
THE CALCIUM BINDING SITE
CONSISTS OF A COMPOUND ASPAR
TICK ACID RESIDUES.
THERE ARE APARTIC ACID RESIDUES
THAT BIND CALCIUM IONS AN
COORDINATE IT WITH PIP-2 THAT IS
ON THE MEMBRANE.
SO THE ACTUAL CALCIUM BINDING
SITE IS A SANDWICH OF CALCIUM
BETWEEN THE TWO SITES.
NOW, THE COST OF DOING BUSINESS
FOR THATCAL YUM BINDING SITE IS
THIS ALOEPHATIC LOOP WHICH MUST
BE INSERTED BECAUSE IT'S THE
ONLY WAY THE CALCIUM BINDING
SITE CAN BE SATISFIED.
SO SYNAPTOTAGMIN INSERTS.
MUTATIONS IN SYNAPTOTAGMIN THAT
ABROGATE THE INSERTION OR
LIKEWISE DON'T ACTIVATE SYNAPTIC
TRANSMISSION.
ONE OR ANOTHER WAY EVERY MODEL
HAS TO ACCOMMODATE THIS AS AN
IMPORTANT ELEMENT OF SYNAPTIC
TRANSMISSION.
THE OTHER THING SYNAPTOT
ACTIONGMIN DOES IN LARGE STUDIES
IS PERTURB MEMBRANES IN ONE OR
ANOTHER WAY.
THE INITIAL EVIDENCE FROM HARVEY
MCMAHAN, TAGMIM IS ADDED IN
EXCESS TO LIPSOMES IT WILL TUBE
LATE THEM IN THE PRESENCE OF
CALCIUM.
THAT REQUIRES INSERTION OF THIS
REGION.
PROBABLY LESS THAN MEGA DOSES IT
DOESN'T TUBE LATE BUT
PHYSIOLOGICALLY PERTURBS IT AND
EVERY LAB WHO STUDIES THIS HAS
FOUND SYNAPTOTAGMIM ACCELERATES
THE RATE OF LIPSOME FUSION WHEN
YOU HAVE SNARES DRIVING IT IN A
CALCIUM DEPENDENT WAY.
IT DOESN'T FUSE BY ITSELF BUT
WILL ACCELERATE PROBABLY A
FACTOR OF 10 TO 100.
BUT VERY SUBSTANTIALLY THE RATE
OF LIPID FUSION, LIPID MEMBRANE
FUSION.
WE DON'T UNDERSTAND EXACTLY HOW
THAT WORKS, PROBABLY IT'S BEEN
CHANGING MEMBRANE INTENTION
ACCORDING TO BRUNGER AND OTHERS
BUT IT'S AN IMPORTANT FACT.
SO IT'S A CALCIUM SENSOR AND
AXEL RANT.
HOW DOES SYNAPTOTAGMIN FIT TYPE
THIS STORY?
THIS IS THE CUTTING EDGE OF THE
FIELD.
BUT WE KIND OF KNOW HOW
SYNAPTOTAGMIN BINDS TO THE SNARE
COMPLEX.
WE KNOW THIS LARGELY FROM THE
WORK OF ALEX BRUNGER, I'LL SHOW
YOU MORE DETAILS.
WHEN IT BINDS IT BINDS ONE PER
SNARE PIN AND WE IMAGINE IT
BINDS CALCIUM FROM THIS ARRAY
BOUND SYNAPTOTAGMIN.
WHEN IT BINDS CALCIUM IT INSERTS
TO THE BILAYER.
WE IMAGINE FURTHER THIS IS OUR
HYPOTHESIS, WHEN I'LL SHOW YOU
SIDE VIEW WHICH IS MORE
EXPLANATORY.
SO NOW YOU SEE THE SYNAPTOTAGMIN
BINDING.
WHEN CALCIUM ENTERS AND BINDS
TO SYNAPTOTAGMIN WILL CAUSE
REARRANGEN'T ONE WAYER ANOTHER
WHICH WE BELIEVE EXERTS
MECHANICAL FORCE ON THIS ARRAY
AND REMOVES A SNARE PIN THERE BY
UNCLAMPING.
THAT'S OUR MODEL, THE AMOUNT OF
EVIDENCE IS RELATIVELY MINIMAL.
AND BUT IT IS IN FACT A SIMPLE
POSSIBLY.
NOW, WHERE DOES THIS COME FROM?
I'LL TRUE TO BUZZ THROUGH THIS
MUCH MORE QUICKLY SEEING THE
HOUR.
WHAT KAREN AND I AND COLLEAGUE
ESPECIALLY DANIELLE CUMEL WHO
DID THE WORK HERE AND BRILLIANT
GUY IS TO SOLVE THE CRYSTAL
STRUCTURE OFR>Ñ4 SNARED COMPLEX.
FOR ALL REASONS I SHOWED YOU
WHEN VAMP IS HALF ZIPPERED
THAT'S WHEN WE THINK ALL THE
ACTION IS OCCURRING FOR
CLAMPING.
I EXPLAINED WHY THAT IS.
PROBLEM YOU HAVE IS YOU CAN'T
GET A CRYSTAL STRUCTURE OF A
DISORGANIZED STATE LIKE A FUSION
INTERMIT OR HALF ASSEMBLED SNARE
COMPLEX.
THE NEXT BEST THING YOU CAN DO
WHICH IS WHAT WE DID IS PRODUCE
A STABLE HALF ZIPPERED SNARE
COMPLEX BY USING JUST THE END
TERMINAL PORTION OF VAMP AN
LEAVING THE REST OUT.
SO THAT PRODUCES A STRUCTURAL
KNEW METIC OF HALF ZIPPERED
SNARE COMPLEX.
WE WERE ABLE TO CRYSTALLIZE THAT
IN COMPLEX WITH COMPLEXIN, NOT
SYNAPTOTAGMIN.
NO ONE GOT ONE TO MY KNOWLEDGE.
WE SOLVED THAT STRUCTURE.
AND WE GOT SOMETHING THAT WAS
MARKEDLY DIFFERENT FROM WHAT
SUDHOFF AN RIDDO FOUND.
THEY FOUND THAT COMPLEXIN LIES
AT ALPHA HELIX IN THE GROOVE
BETWEEN SYNTAXIN AND VAMP
CONTACTING BOTH OF THEM, THIS IS
THE SEN TRILLION HELIX PORTION,
ACCESSORY HELIX HAD NO CONTACTS
WITH THE SNARE COMPLEX BUT HELIX
RUNS PARALLEL TO THE SNARE
COMPLEX.
THAT'S NOT AT ALL WHAT WE FOUND.
WE FOUND THE OPEN CONFIRMATION.
IN CONTRAST TO THE OTHER
CONFIRMATION POST FUSION
REPRESENTING THE FULLY ZIPPERED
SNARE COMPLEX WE CALL CLOSED.
OPEN GOES OFF AS 45-DEGREES.
THE COMPLEXIN HELIX IS ISOMORE
FIXED.
'S THE SAME HERE AND HERE EXCEPT
FOR THE WAY IT LIES ON THE SNARE
COMPLEX, IT'S BASICALLY THE
SAME.
BUT NOW GOES OFF AT 45-DEGREES.
THAT POSED A PROBLEM FOR US
BECAUSE I WAS TELLING YOU THE --
ALL THE GENETICS SAID THE
ACCESSORY HELIC DOES CLAMPING.
BUT WHAT'S CLAMPED IS THE
ASSEMBLING OF MEMBRANE PROXIMAL
WOULD BE HERE, PORTION OF THE
SNARE COMPLEX ASSEMBLED LAST,
HOW CAN THIS HELP -- HOW CAN
THIS INTERFERE WITH ZIPPERING OF
THIS WHEN THEY'RE ACTUALLY
DIVERGING AWAY FROM EACH OTHER.
THE ANSWER COMES FROM THE
CRYSTAL PACKING.
WHEN WE LOOK AT LAYER OF CRYSTAL
WE SEE A SNARE PIN, THE MEMBRANE
ANCHORS WOULD BE AT THIS END,
THE SYNAPTIC VESICAL WOULD BE
ABOVE AS IN THE CARTOON, THE
PLASMA MEMBRANE IN THE PLAIN
BELOW, HERE IS THE HALF ZIPPERED
VAMP.
NOW WHAT YOU SEE THE COMPLEXIN
CENTRAL HELIX LAUNCHING AN
ACCESSORY HELIX, BUT THAT
ACCESSORY HELIX IN THE OPEN
CONFIRMATION ACTUALLY BINDS IN
THE SAME GROOVE THIS V SNARE
WOULD IF IT CONTINUES TO ZIPPER.
EXACTLY AS I CARTOONED IT.
THIS IS THE BASIS FOR THE ZIG
ZAG ARRAY AND IDEA OF
INTERMOLECULAR CLAMPING AS THE
PRINCIPLE FOR CLAMPING OF
SYNAPTIC TRANSMISSION TO ALLOW
SIN CHRONICITY.
ANY CRYSTALOGRAPHER TELLS YOU
THIS IS GOOD BUT HOW DO YOU KNOW
THIS ISN'T A CRYSTALZATION OAR
FACT?
I HAD NEVER HEARD OF A
COUNTRYALZATION ARTIFACT.
-- CRYSTALZATION ARTIFACT.
I THOUGHT AS SOON AS YOU GET A
CRYSTAL STRUCTURE EVERYBODY
CONGRATULATES YOU.
PUBLISHES YOUR PAPER.
NO, THEY SEND YOU BACK HOME
THAT'S WHERE WE BIOCHEMISTS
START COMING IN TO THE PICTURE
BECAUSE HOW DO WE KNOW THIS
DIDN'T OCCUR AS A RESULT OF THE
CRYSTALLIZATION?
WE KNOW.
HOW?
BECAUSE WE CAN ISOLATE COMPLEXES
IN SOLUTION AND WE OBSERVE TO
BEGIN WITH THIS OPEN
CONFIRMATION EXISTS.
THIS WAS WORK BY CRYSTAL KUMAR
AND DANIEL RADOFF IN MY LAB.
NO DETAILS GIVEN THE TIME.
WE USE FRET ENTER INTERMOLECULAR
FRET.
WE FORM COMPLEXES OF COMPLEXIN
AND THE SNARE COMPLEX.
AND PUT A THREAT ACCEPTTOR ON
SNAP 25 ON THE BASE OF THE
COMPLEX AND TWO POSITIONS O
MORE.
IN THE COMPLEXIN ACCESSORY
HELIX, WE PLACE THE COGNATE
FLUORESCENT PROBE.
THIS ALLOWS US TO READ THE
DISTANCE THROUGH FRET, THE
SIGNAL WILL GO UP IN THE CLOSE
CONFIRMATION ON OPEN
CONFIRMATION.
AS YOU CAN SEE WE OBSERVE VERY
STRONG FRET SIGNAL WHEN WE HAVE
THE FULL LENGTH VAMP HERE BUT
WHEN WE HAVE THE FIRST 60
RESIDUES OF VAMP THE HALF
ZIPPERED STATE NOW WE GET OPEN.
I HOPE THAT'S
HOW DO WE KNOW THESE
CONFIRMATIONS ARE WHEY THEY SAY?
WE CAN TAKE THE FRET NUMBERS AN
CRUNCH THE NUMBERS.
AND ACTUALLY WE PREDICT WITHIN
10% SYSTEMATIC THE CRYSTAL
COORDINATES OF THESE -- THIS
POSITION, THIS POSITION, THIS
POSITION AND THAT POSITION
RELATIVE TO THAT POSITION IN THE
TWO CRYSTALS TWO TYPES OF
CRYSTALS OPEN AN CLOSE IN THREE
FORMS.
SO WE'RE VERY CONFIDENT THAT
THIS IS THE NATURAL STATE AND
SOLUTION, THEREFORE THE
CRYSTALZATION DID NOT CAUSE THE
OPEN STATE, THE OPEN STATE HAD
TO BE ACCOMMODATE MISDEMEANOR
THE CRYSTAL.
THE OTHER POTENTIAL CONCERN IS
HOW DO WE KNOW THIS
TRANSINTERACTION BETWEEN THE
ACCESSORY HELIX AND T SNARE AT V
SNARE BINDING SITE OCCURS
INDEPENDENT OF CRYSTAL?
WE KNOW THAT BECAUSE WE CAN
MEASURE IN SOLUTION NOW THAT WE
KNOW TO LOOK FOR IT.
AGAIN, THIS IS PUBLISHED IN
2011, IN NATURE STRUCTURAL
MOLECULAR BIOLOGY, I NEED TO
UPDATE THE SLIDE.
IF YOU MIX COMPLEXIN AND P THE
SNARE COMPLEX WITH A HALF ZIPPER
ED SNARE EXACTLY WHAT WENT
INTO THE CRYSTAL BUT WITH ITS
COMPLEXIN ACCESSORY HELIX SITE
PRE-BOUND AN PRE-BLOCKED BY
CENTRAL HELIX, I MEANT CENTRAL
HELIX BINDING SITE PRE-BLOCKED
SO ONLY THE HYPOTHETICAL
TRANSSITE INVOLVING THE TERMINAL
T SNARE IS AVAILABLE.
WE GET STOIC METRIC BINDING.
15 MICROMOLAR BINDING CONSTANT,
NKT BINDING ENERGY, A NUMBER
WORTH REMEMBERING.
THAT IS CLOSELY LINKED TO THE
ACTIVATION FOR MEMBRANE FUSION.
NOW VERY IMPORTANTLY, WE MADE
MUTATIONS -- I CAN SEW -- WE
MADE MUTATIONS IN ACCESSORY
HELIX INCREASE OR DECREASE THE
BINDING ENERGY HERE.
YOU CAN SEE HERE POINT MUTATION
IN THE ACCESSORY HELIX RIGHT
HERE THAT ELIMINATES BEHINDING
>> SO WHAT DO WE PREDICT?
NORMAL GENE THIS GENE TESTED
PHYSIOLOGICALLY SHOULD CLAMP
BETTER THAN NORMAL AND SHOULD
REDUCE SPONTANEOUS FUSION THIS
IS WHAT WE SEE IN A CONTROL
ANIMAL, WHAT THEY SEE REALLY, IT
OCCURS T A COUPLE PER SECOND
MORE OR LESS AS DESCRIBED.
IF YOU KNOCK OUT COMPLEXIN THE
RATE IS UP TO PREVENT
SPONTANEOUS RELEASE.
A CLAMP P IF YOU REMOVE IT IF
YOU REMOVE THE CLAP THAT
PREVENTS THE SPONTANEOUS
RELEASE, WHAT HAPPENS TO
SPONTANEOUS RELEASE?
GOES UP.
THAT'S EXACTLY WHAT HAPPENS
HERE.
COMPLEX,N IS THE CLAMP.
IF WE MUTATE RESIDUES THAT FACE
THE INSIDE CONTACTING REGIONS
FOR THE T SNARE, WHEN WE DO
THAT, THEN OR IF WE DISRUPT THE
HELIX NOW ACTUALLY -- WE PUT IN
THE HUMAN COMPLEXIN WE ACTUALLY
HAVE NO AFFECT.
EVEN THOUGH IT'S THERE, IT'S
THERE AT THE SYNAPSE, IT DOESN'T
CLAMP.
IT CLAMPS NOT QUITE AS WELL.
WE'RE TRYING TO UNDERSTAND THIS
AS DROSOPHILA GENE IF WE PUT IN
ACCESSORY HELIX MUTANT THAT HAS
A FIVE TIMES HIGHER BEHINDING
ENERGY WE GET FIVE TIMES LOWER
SPONTANEOUS RELEASE.
SO TO SUMMARIZE THEN, THIS
INTERACTION IN THE CRYSTAL
STRUCTURE THAT WE BELIEVE IS THE
STRUCTURAL BASIS OF CLAMPING,
THAT INTERACTION MUST BE
CONTROLLING SPONTANEOUS RELEASE
BECAUSE AS WE RATCHET UP AND
DOWN THAT INTERACTION BY THE
SAME LOGIC AS TOM SUDOFF
RATCHETING UP AND DOWN CALCIUM
BINDING THAT RATCHETS UP AND
DOWN SYNAPTIC NEUROTRANSMITTER
RELEASE, THAT'S WHY IT'S THE
CALCIUM SENSOR.
THIS MUST BE THE CLAMPING
INTERACTION IF WE RATCHET UP AND
DOWN CLAMPING GETS RATCHETED UP
AND DOWN IN PHYSIOLOGICAL
SYSTEM.
SO THERE'S NO DOUBT THIS
TRANSINTERACTION THAT GIVES RISE
TO THIS ZIG ZAG ARRAY FROM THE
COUNTRYAL STRUCTURE IS THE
STRUCTURAL BASIS OF CLAMPING
WHICH MUST THEN OCCUR IN THE
HALF ZIPPERED STATE.
SO THIS IS A VERY IMPORTANT
EXPERIMENT I THINK FOR THE
ENTIRE CASE AND FOR THE ENTIRE
MODEL.
DO WE KNOW THAT THE ZIG ZAG
ARRAY EXISTS IN THE WAY IT DOES
IN THE CRYSTAL COURSE?
WE DOPE KNOW.
WE'RE INVESTIGATING.
IT MAYBE MORE TRUNCATED.
MAYBE INVOLVES TWO SNARE
COMPLEXES.
I DON'T KNOW AT THIS POINT.
BUT THAT INVOLVES CLAMPING
INVOLVES TRANSINTERACTION SEEMS
CLEAR.
HIGH CONCENTRATION HERE AS THEY
ARE IN THE CRYSTAL.
IN FACT, WHEN WE CALCULATE
ESTIMATE WHAT IT'S LIKE IN THE
SPACE HERE IT'S ACTUALLY LOWER
THAN THE CRYSTAL THAN IN THE
SPACE.
WHERE YOU HAVE TWO CLOSELY
OPPOSED MEMBRANES SO IT'S LIKELY
THAT WE HAVEN'T PROVEN THIS
ARRAY IS SOME SIGNIFICANT EXTENT
PROBABLY 10, 15 COPIES OF THE
SNARE PIN WE'RE GUESSING.
A VERY IMPORTANT POINT A VERY
IMPORTANT POINT IS THAT THIS IS
THE PRE-FUSION STATE IN THE HALF
ZIPPERED STATE, THIS IS WHAT
EVERYBODY IMAGINES THE FUSION
PORE MUST LOOK LIKE, IT HAS TO
BE CIRCULAR, IF IT HAS MULTIPLE
SNARES THEY HAVE TO BE ARRANGED
WHETHER BY INTENT OR NECESSITY.
SO -- AND THE OPEN STATE HERE,
OF THE COMPLEXIN OCCURS MUST GO
THROUGH A TRANSITION THEN
BETWEEN OPEN AND CLOSE, THERE
MUST BE A TRANSITION TO START
AGAIN BETWEEN OPEN AND CLOSED
STATE OF COMPLEXIN BECAUSE THIS
IS WHAT WE GET WHEN IT'S IN THE
CLAMP STATE AND THIS IS WHAT WE
SEE OR WHAT IS SEEN IN THE POST
FUSION STATE.
SOMEWHERE IN THERE THERE IS A
SWITCH.
NEW YORK CITY I THINK YOU CAN
SEE IN ORDER FOR THIS VAMP TO
CONTINUE TO ZIPPER THAT
ACCESSORY HELIX HAS TO GET MOVED
OUT WAY.
THAT'S OBVIOUS.
BUT WHEN THAT OCCURS, THERE IS
NOTHING THEN WHEN THAT HAPPENS
THERE'S NOTHING TO PREINVENTORY
THIS ZIPPERING.
IF YOU WERE TO TAKE ALL THESE
OPEN STATES AN CONVERT TO
CLOSED, I THINK YOU CAN SEE THAT
THE ZIG ZAG ARRAY CAN NO LONGER
FORM.
THE ZIG ZAG ARRAY THE ONLY FORM
IF THE OPEN CONFIRMATION AND THE
CLOSED THE ACCESSORY HELIX IS
SATISFIED WITH ITS OWN SNARE
COMPLEX AND NO LONGER CAN
INTERACT WITH ANOTHER ONE.
SO THIS OPEN TO CLOSE SWITCH IS
CLEARLY THEN WHAT WILL BE
DRIVING THE ACTIVATION PROCESS.
I WON'T HAVE TIME TO GO INTO
THIS, IT'S IN OUR PAPERS IF
YOU'RE INTERESTED BUT IT TURNS
OUT FOLLOWING RESIDUE 60 IN
VAMP, THERE'S RESIDUE 1, THERE'S
60, BETWEEN 60 AND 67 THERE ARE
TWO VERY SPECIAL TURNS OF THE
HELIX.
THAT CONTAIN THREE ASPAR TICK
ACID RESIDUES.
THOSE ACTUALLY FORM AN
INTERACTION WITH THE ACCESSORY
HELIX HERE.
THAT INTERACTION CANNOT OCCUR
WHEN THOSE TWO TURNS ARE NOT YET
FOLDED.
WHEN THOSE TURNS ARE FOLDED,
THEY THEN CREATE THE BINDING
SITE THAT IS DIFFERENT BETWEEN
THIS STRUCTURE AND THIS
STRUCTURE AND THEY PULL THE
COMPLEXIN ACCESSORY HELIX DOWN.
WHAT HAPPENS IN FACT WE THINK IS
THAT WHEN ANY ONE OF THESE
ACCESSORY HELICES FLUCTUATES OUT
LONG ENOUGH, THIS VAMP SAY THIS
ONE HERE ZIPPERS, WHEN IT
ZIPPERS TO HELICES THAT CREATES
A BINDING SITE, WITH COMPLEXIN,
COMPLEXIN IS SWITCHED FROM OPEN
TO CLOSED WHEN IT DOES THAT IT
RETRACTS FROM THIS GUY.
WHEN THIS RETRACTS THEN THAT
VAMP GETS ZIPPER AND PULLS DOWN
THIS GUY.
LIKE A HOUSE OF CARDS IT GOES
DOWN.
WE HAVE TESTED THAT MUTATING THE
APARTIC ACID RESIDUE AND WHEN WE
DO THAT YOU GET IN VAMP AND YOU
GET PERFECTLY GOOD FUSION IN AND
OF ITSELF BUT YOU LOSE AT LEAST
IN OUR IN VITRO SYSTEM THE
ABILITY TO ACTIVATE FROM
CALCIUM.
WE'RE TESTING THAT IN A
PHYSIOLOGICAL SYSTEM IN
NEUROMUSCULAR JUNCTION THAT'S
OUR CURRENT VIEW.
SO I JUST WANT TO LEAVE YOU THEN
WITH OUR HYPOTHESIS OF HOW
ACTIVATION MAY WORK WHICH IS
LARGELY BASED ON COMBINING WHAT
I HAVE SHOWN FROM OUR LAB AND
VERY ELEGANT WORK THAT AXEL
BRUNNER AN COLLEAGUE AT STANFORD
USING FRET EXTENSIVELY TO
MEASURE POSITIONING OF
SYNAPTOTAGMIN ON THE SNARE
COMPLEX.
IT'S MISSING A CRYSTAL STRUCTURE
BOUND TO A SNARE COMPLEX IN ANY
STATE OF ASSEMBLY.
EVEN HIGH RESOLUTION PICTURE.
IF ANYBODY HAS AMBITION IN THIS
FEEL THAT'S HELPFUL TO HAVE.
BUT BASED ON HIS MOLECULAR
DYNAMIC MODEL AND BIOCHEMICAL
DATA CONSISTENT WITH THIS, IT
APPEARS THAT SYNAPTOTAGMIN BINDS
TO THE SNAP 25 SIDE OF THE
ASSEMBLING SNARE PIN.
IT BINDS ONE PER SNARE PIN.
STOICHIOMETRY, ONE ACTIVATOR PER
SNARE PIN.
IT BINDS TO THE SNAP 25 FACE.
THERE ARE FOUR HELICES IN THE
BUNDLE, TWO ON ONE SIDE, TWO ON
THE OTHER.
TWO ON ONE SIDE ARE THE TWO FROM
SNAP 25.
THEY SEEM TO BIND THIS
SYNAPTOTAGMIN.
THE OTHER TWO IS WHERE THE PLANT
SIDE WHERE THE CLAMPING OCCURS,
THAT IS WHERE VAMP AND SYNTAXIN
ARE WHERE THE ACCESSORY HELIX.
THE CENTRAL HELIX TO ALL THE
ACTION THAT I HAVE JUST BEEN
SHOWING YOU IS OCCURRING ON THE
OPPOSITE SIDE OF THE SNARE
BUNDLE WHERE WHERE SYNAPTOTAGMIN
BINDS.
WHEN IT BINDS THIS WAY
CONVENIENTLY THIS IS SHOWN
FACING THE VESICAL MEN BRAIN IT
FACES THE MEMBRANE AND WE DONE
KNOW IF ANY (INDISCERNIBLE) SO
ALL THAT NEEDS TO OCCUR WHEN
CALCIUM ENTERS IS FOR THIS
SYNAPTOTAGMIN TO BE ORIENTED BY
THE MEMBRANE.
I HAVE SHOWN YOU ANYTHING
FRAMEWORK THAT GOT REMOVEDDED
FROM.
THE SIMPLEST MODEL CARRIES THIS
OUT WE FORMED WITH TWO
NANODISABLES WHICH ZIPPER TO A
LARGE DEGREE BUT CAN'T FUSE
BECAUSE OF CONSTRAINTS.
WE PUT SYNAPTOTAGMIN ON IT AND
WE HAVE DONE STOP FLOW MEASURING
ON A SCALE OF MILLISECONDS IN
FACT THE INSERTION OF THIS LOOP
OF SYNAPTOTAGMIN TRIGGERED BY
CALCIUM AND ASKED WHETHER IT
REMAINS BOUND TO THE SNARE
COMPLEX AS IT INSERTS.
BECAUSE IF SYNAPTOTAGMIN IS
GOING TO ACTIVATE BY PHYSICALLY
DOING WORK ON THE SNARE COMPLEX
REMOVING IT FROM THE PLAIN, IT'S
PLAINER ARRAY STRUCTURE CLEARLY
NEEDS TO HANG ON DURING THIS
INSERTION PROCESS AND THAT IS IN
FACT THE CASE.
HERE WE LOOK AT FLUORESCENCE
ORING INSESSION OF ALOETHATIC
LOOP BETWEEN A AND V DOMAIN AND
SNAP 25 WHICH BECOMES ABSOLUTELY
INVARIANT.
BY THE WAY ALSO FOR THOSE WHO
MAYBE AFICIONADOS THE A AND B
DOMAIN DON'T MOVE WITH RESPECT
TO EACH OTHER DURING THIS POWER
STRUGGLE SO THERE IS A POWER
STROKE WHICH SYNAPTOTAGMIN
INSERTS TO THE BILAYER SHOWN
GENETICALLY TO BE NEEDEDTOR
PASSAGE OF CALCIUM SIGNAL TO THE
SNARE.
IT'S PHYSICALLY BOUND TO THE
SNARE AND BASED ON THIS IN VITRO
WORK MAINLY THE ONLY TENABLE
MODEL BECAUSE THE
SYNAPTOCONFIRMATION A AND B
DON'T CHANGE THEIR DISTANCE, A
MECHANICAL FORCE IS EXERTED AND
WE CAN'T PROVE TODAY THAT THAT
MECHANICAL FORCE IS TRANSDUCED
INTO REMOVING THE ACCESSORY
HELIX FROM THE T SNARE BEHINDING
SITE THAT CAUSES THE INHIBITION
BUT OBVIOUSLY CAN SEE THAT
THAT'S A VERY TENABLE HYPOTHESIS
THAT'S THE ONE WE'RE FOCUSED ON.
IT'S GENERAL TECHILY AND
KINETICALLY.
THIS IS MY LAST SLIDE.
THE ACTIVATE ENERGY TO REMOVE A
SNARE PIN CAN REQUIRE BREAKING
TWO INTERACTIONS.
IT'S ENTERACTING WITH ONE SNARE
PIN AND IN DISARRAY WITH
ANOTHER.
THIS INTERACTION CAN BE BROKEN
BY SO FOR THIS INTERACTION THAT
WILL BREAK TO THIS ONE OR 10 KT
WILL BREAK THIS ONE.
IF YOU PULL OUT IF YOU HAVE A
FLUCTUATION IF YOU HAVE 10-KT
ONLY YOU GET FLUCTUATIONS HERE
OPT ORDER OF ABOUT TWO
MICROSECONDS ACCORDING TO SINGLE
MOLECULE TYPES OF CALCULATIONS.
DOWN HERE ACCORDING TO SOMEBODY
OR OTHER RELATIONSHIP WHICH MY
PHYSICIST COLLEAGUE IS TELLING
ME ABOUT AND WHICH I MIGHT ONCE
HAVE UNDERSTOOD.
SORRY TO BE BLAH SAY ABOUT THAT
BUT THE PHYSICISTS AGREE THE
FLUCTUATION OCCURS IN 2 TO 20
MICROSECONDS, NOT LONG ENOUGH TO
BE PERSISTENT.
SO THAT ALLOWS DETERMINED ACT
INVESTIGATION BY REMOVING TWO OF
THESE POINTS WHEN YOU REMOVE
TWO, WHEN YOU LOOK YOU'LL SEE
THE WHOLE THING FALLS APART LIKE
DOMINOES BUT IF YOU REMOVE IT
TAKES 20 KT TO CAUSE ACTIVATION.
THE SIMPLEST HYPOTHESIS IS THAT
THIS+ THE ACTUAL ENERGY RELEASED
WHEN IT BINDS CALLS YUM PLUS PIP
AT RELEVANT CONCENTRATION 45 KT.
IS IT FULLY AVAILABLE TO TO BE
CHANNELED?
NO, DID NOT KNOW THAT, WITH WE
DONE KNOW THAT BUT AT LEAST IT'S
ATENABLE HYPOTHESIS.
AND KINETICALLY TENABLE AS WELL.
SORRY FOR THE BREATHLESS FINISH.
I WOULD LIKE THE JUST THANK THE
COLLEAGUES WHO ARE MOST
CRITICALLY IMPORTANT FOR THIS
WORK, THE EXPERT CRYSTALOGRAPHY
DANIELLE KUMEL AND CAPE RYAN ISH
PROFESSOR IN YALE CELL BIOLOGY
DEPARTMENT, THE
ELECTROPHYSIOLOGY THAT WAS SO
IMPORTANT ESTABLISHING THE
PHYSIOLOGICAL RELEVANCE AT MIT.
AND WORK IN THE FIRST INSTANCE
COMPLEXIN CLAMPS IN A DIFFERENT
STATE THAT GIVES US THE CLUE HOW
TO DESIGN THE MOLECULE FOR THE
CRYSTAL STRUCTURE FOR THE
PHYSICIST,'S IMPORTANT IN ALL
COLLABORATIONS.
MORE RECENTLY THE OBSTACLE WORK
WITH ANOTHER PROFESSOR AT YALE
AND FOLKS FROM MY LAB I
MENTIONED I BELIEVE AS I HAVE
GONE THROUGH THE WORK IN THEIR
PARTICULAR CONTRIBUTION.
SO THANK YOU ALL VERY MUCH.
[APPLAUSE]
>> WE'LL TAKE QUESTIONS AFTER
THE CALL CLEARED OUT PEOPLE WHO
NEED TO GO RIGHT AWAY.
>> I ONLY HAPPY TO DO IT HERE OR
GO TO THE RECEPTION.
MAYBE HARDER TO DO THAT.
>> QUESTIONS.
>> THANK YOU.
VERY, VERY EXCITING AND ALSO IT
HAPPENS IN THE IMMUNOLOGICAL
EXCEPT FOR SLOWER PACE.
MY QUESTION AND MAYBE SUGGESTION
IS YOU MENTIONED THE END
TERMINUS IS ACTUALLY STARTING
THE WHOLE GAME FOR STRUCTURE OF
AND SIGNAL TO THE END TERMINAL.
IS THERE ANY INFORMATION KNOWN
ABOUT THE END TERMINAL
COMPOSITION FOR GROUP THAT IT'S
--
>> WHAT'S THE QUESTION THEN?
>> THE COMPOSITION OF THE END
TERMINAL AND THE C TERMINAL,
CHANGES AND THE CHARGE --
>> WE SHOULD DISCUSS PRIVATELY
BUT COMPOSITION OF THE AMINO
ACIDS ISN'T LIKELY TO CHANGE, IF
THAT'S WHAT YOU MEAN.
IS THERE ANOTHER QUESTION?
>> OKAY.
>> YES.
>> IT SEEMS LIKE ONE OF THE
CRITICAL THINGS IN THE
MEASUREMENT OF THE SYNCHRONOUS
PHENOMENA AND TIME DEPENDENT ARE
THE TOOLS THAT YOU USE AND X-RAY
COUNTRYALOGRAPHY ARE A SNAP SHOT
THAT HAPPENS OVER A PERIOD OF
TIME.
SOME SECONDS OR NANOSECONDS.
IF YOU HAD A WISH LIST OR -- OF
A NEW TOOL THAT YOU COULD USE OR
MAYBE IN EXISTENCE, WHAT DOES
THAT IT WILL LOOK LIKE?
TWEEZERS IS THERE ANYTHING KNOWN)/P
ABOUT THE LIPID ENVIRONMENT --
AND HOW THAT MIGHT ASSIST.
THISES WHO FUSION PROCESS?
>> GOOD QUESTION.
ASIDE FROM PIP IS A BEING ASIDE.
THAT IS ABSOLUTELY REQUIRED
PHYSIOLOGICALLY, REQUIRED IN
VITRO SYSTEMS FOR THE MAXIMUM
EFFECT, IT IS VERY,VERY
IMPORTANT.
OTHER THAN THAT WE'RE
UNFORTUNATELY LEFT WITH THE
IMAGINATION THE SNARES ARE
LARGELY UNCARING ABOUT THE SPEED
OF LIPIDS, IT WILL GO UP OR DOWN
BUT NOT DETERMINING.
THERE'S SOMETHING IMPORTANT IN
THE CLUSTERING THE T SNARES SEEM
TO BE IN MANY DIFFERENT CELLS IN
SO CALLED LIPID RAS OR DOMAINS
THAT ARE CHOLESTEROL DEPENDENT,
YOU DON'T KNOW ENOUGH ABOUT
THEM.
SO I DON'T WANT TO SAY -- I
ACTUALLY TO THINK THEY'RE QUITE
IMPORTANT, MAYBE THE (INAUDIBLE)
ITSELF IS A LIPID RAS. THERE'S
SUGGESTIONS ALONG THOSE LINES SO
THERE IS A VITAL IMPORTANCE BUT
THE -- NEITHER IN VITRO SYSTEMS
NOR THE CRUDE TOOLS AVAILABLE, I
DON'T MEAN TO SAY GENETIC IS
CRUDE BUT RELATIVE TO THE TYPE
OF PHYSIOLOGY THAT KNOCKING
SOMETHING OUT, IT'S ALL
RELATIVELY PROVEN SO WE DONE
KNOW.
I WILL LIKE TO KNOW.
>> DO YOU HAVE ANY INSIGHT TO
WHAT HAPPENS IN ASYNCHRONOUS
RELEASE WHICH MAYBE IMPORTANT
FOR INSULIN SECRETION IN
>> DOES NOT REQUIRE
SYNAPTOTAGMIN.
I DON'T HAVE PERSONAL KNOWLEDGE,
MY IMPRESSION FROM THE
LITERATURE IS THAT SYNAPTOTAGMIN
IS NOT THE CALCIUM SENSOR, MY
IMPRESSION IS THERE'S SOME
SENTIMENT THERE'S A RELATED
PROTEIN CALLED DOCK 2 THAT MAYBE
THE CALCIUM SENSOR BUT MY OTHER
IMPRESSION IS CONTROVERSIAL
THERE. IS A CALCIUM SENSOR.
THAT'S CLEAR.
>> WHAT IS COMPLEXIN DOING IN
THAT SITUATION?
>> I DON'T KNOW.
I WOULD PREDICT PROBABLY
NOTHING.
I WOULD GUESS IT'S NOT INVOLVED.
IN FACT, YOU CAN GET CALCIUM
DEPENDENT -- THE NICEST
EXPERIMENT HERE, THERE'S A LOT
OF NICE EXPERIMENTS BUT TO MY
MINE THE NICEST IS IN VITRO
EXPERIMENT WITH PURE PROTEINS BY
THOMAS SULNER LAST YEAR BECAUSE
IT -- EWE ABSOLUTE CONTROL OF
EVERYTHING.
WHAT HE SHOWS IS IF YOU LEAVE
COMPLEXIN OUT BUT YOU HAVE STILL
HAVE PIP 2 SYNAPTOTAGMIM AND
SNARES YOU GET VESICAL DOCKING
AND RELEASE THAT'S CALCIUM
DEPENDENT.
BUT THE AMOUNT OF FUSION IN THE
ABSENCE OF CALCIUM GOES UP VERY
DRAMATICALLY, THE AMOUNT OF
VESICAL FUSION THAT YOU GET WHEN
YOU ADD CALCIUM IS -- BRINGS YOU
UP TO 100% BUT LESS -- FAR TO GO
BECAUSE YOU FUSED 20%.
SO THERE'S LESS RELEASE IF YOU
WANT TO THINK ABOUT IT THAT WAY.
INSTEAD OF IT GETTING DONE LESS
THAN SECOND IT DRIBBLES OUT 10,
20 SECONDS, NO FUSION IN THE
ABSENCE OF CALCIUM, TOTAL HI
CLAMPED.
100% RELEASE AND ALL WITHIN THE
FIRST SECOND.
ASYNCHRONOUS GOES TO
SYNCHRONOUS.
ASYNCHRONOUS DEPENNING HOW IT
IS, YOU CAN GET THAT WITH
SYNAPTOTAGMICS N ALONE.
IT'S LIKELY AN IMPEDIMENT TO
MEMBRANE FUSION BY SITTING
BETWEEN THE TWO MEMBRANES.
SO IT SLOWS THE TERMINALS.
LET'S ADJOURN TO THE LIBRARY AND THANK YOU FOR COMING