membrane fusion 2

What is membrane fusion

The merging of two lipid bilayers into one continuous membrane

What protein family drives membrane fusion

SNARE proteins

What are t SNAREs

Syntaxin and SNAP 25 on the target membrane

What are v SNAREs

Synaptobrevin on the vesicle membrane

What is the SNARE complex

A four helix coiled coil formed by v and t SNAREs

How does the SNARE complex assemble

By zippering from N terminus to C terminus

What is the energy source for membrane fusion

Energy released from SNARE coiled coil formation

What barrier must be overcome for fusion

The hydration barrier between membranes

What is hemifusion

An intermediate where outer lipid leaflets mix

What experiment showed SNAREs are sufficient for fusion

Liposome reconstitution assays

What did inside out SNARE experiments show

SNAREs alone can drive cell cell fusion

What happens when neurotoxins cleave SNAREs

Complex forms but fusion does not occur

What does this show about SNAREs

A physical link to the membrane is required

What animal model was used to study SNARE function

Knockout mice

How was synaptic transmission measured

Evoked postsynaptic potentials

What happens when syntaxin is knocked out

Near complete loss of neurotransmission

Why is the region near the membrane important in syntaxin

It provides leverage for fusion

What happened when the six amino acid linker was removed

No rescue of fusion activity

Is the syntaxin transmembrane domain essential

No it can be replaced by a lipid anchor

Do SNARE transmembrane domains drive lipid mixing

No they are not directly involved

What question remained after SNARE studies

What proteins drive lipid mixing efficiently

What genetic system identified additional fusion factors

Yeast sec mutant screens

How were sec mutants isolated

By density increase due to blocked secretion

What is Sec1

A late acting secretion protein essential for fusion

What are Sec17 and Sec18

SNAP and NSF

What family does Sec1 belong to

SM proteins

What is the mammalian homolog of Sec1

Munc18

What organism identified Munc18 via movement defects

C elegans

What happens without Munc18

Membrane fusion fails at a late step

What do liposome assays show about Munc18

It accelerates fusion

When does Munc18 act

During SNARE complex priming

What does the Sec1 Munc18 structure reveal

It stabilizes and activates SNARE complexes

What does Munc18 remove

Autoinhibition of syntaxin

What type of fusion is synaptic vesicle fusion

Fast and calcium triggered

What protein is the calcium sensor

Synaptotagmin

Where is synaptotagmin located

On synaptic vesicles

How many calcium binding domains does synaptotagmin have

Two C2 domains

What happens when calcium binds synaptotagmin

C2 domains insert into the membrane

What protein clamps SNARE zippering

Complexin

What is the role of complexin

Allows docking but blocks final fusion

How is the fusion clamp released

Synaptotagmin displaces complexin after calcium binding

What is the sequence of synaptic fusion

Priming docking calcium trigger fusion

What proteins recycle SNAREs after fusion

NSF and SNAP

What is membrane tethering

Long range capture of vesicles before docking

What proteins control tethering

Rab GTPases

How many Rab proteins are in mammals

About sixty

How are Rabs attached to membranes

Geranylgeranyl lipid anchors

What cycle controls Rab activity

GTP GDP cycle

What do active Rabs recruit

Tethering factors

Which Rab is found on synaptic vesicles

Rab3

What is the active zone

A protein rich presynaptic region for fusion

What protein links Rab3 to calcium channels

RIM

What is the role of Munc13

Priming SNAREs and collapsing tethers

What is the function of RIM binding protein

Organising calcium channels and fusion machinery

What is the core universal fusion machinery

SNAREs and SM proteins

What experiments defined minimal fusion machinery

Liposome reconstitution experiments