Synaptic Vesicle Fusion and SNARE Complexes

These flashcards cover key vocabulary terms relating to synaptic vesicle fusion, SNARE complexes, and associated proteins, designed to aid in studying and understanding synaptic physiology.

SNAP-25

A protein that participates in synaptic vesicle fusion by forming part of the SNARE complex.

Synaptobrevin

Also known as VAMP, a protein involved in vesicle fusion and SNARE complex formation.

Syntaxin

A t-SNARE protein that plays a crucial role in the docking of synaptic vesicles.

Primed vesicles

Vesicles that are prepared for fusion and release at the synapse.

SNARE complex

A protein complex formed between SNAP-25, synaptobrevin, and syntaxin, critical for vesicle fusion.

Fusion competent

The state of vesicles that are ready to fuse with the presynaptic membrane.

Closed syntaxin configuration

A structural state of syntaxin where the SNARE binding domain is hidden, preventing complex formation.

Open syntaxin configuration

The structural state of syntaxin that allows SNARE complex formation.

UNC-13

A protein that binds to the N-terminus of syntaxin and promotes SNARE complex assembly.

Vesicle docking

The process by which synaptic vesicles attach to the presynaptic membrane in preparation for fusion.

Synaptic vesicle (SV)

A small, membrane-bound structure containing neurotransmitters, which is essential for synaptic transmission.

Calcium influx

The entry of calcium ions into the presynaptic terminal, triggering vesicle fusion.

Synaptotagmin I

A calcium-binding protein that regulates vesicle fusion in response to calcium.

Calcium binding

The interaction of calcium ions with proteins that play a role in neurotransmitter release.

DAG

Diacylglycerol, a molecule that regulates transitions in SNARE complex assembly states.

PIP2

Phosphatidylinositol 4,5-bisphosphate, a phospholipid that plays a role in membrane dynamics and protein interactions.

Presynaptic membrane

The membrane of the transmitting neuron where vesicles fuse to release neurotransmitters.

SV docking defects

Issues that arise in the attachment of synaptic vesicles to the presynaptic membrane, leading to impaired neurotransmitter release.

Munc13 ring

A structure that promotes SNARE complex assembly at synapses.

Clamped SNAREpins

State of SNARE complexes where they are held together, awaiting the release triggered by calcium.

Exocytosis

The process by which vesicles release their contents into the extracellular space.

Synchronous release

The coordinated release of neurotransmitters from multiple vesicles in response to an action potential.

High-pressure freezing technique

A method used to preserve synapses in a physiological state for imaging and analysis.

Synaptic cleft

The space between the presynaptic and postsynaptic membranes where neurotransmitters are released.

Calcium-gated channels

Voltage-gated channels that open in response to action potentials, allowing calcium entry.

SNARE zippering

The process by which the SNARE complex tightens, promoting membrane fusion.

C2B domain

A region of synaptotagmin that interacts with the target membrane upon calcium binding.

PM dimple

The inward curve of the plasma membrane caused by synaptotagmin binding.

Action potential

An electrical signal that travels along a neuron, leading to neurotransmitter release.

Primed vesicle state

The condition of vesicles that are ready and waiting at the presynaptic membrane for a calcium signal.

Munc13/UNC-13 interaction

Binding of the Munc13 protein to syntaxin, necessary for vesicle priming.

Synaptic transmission

The process through which signaling is conveyed between neurons via neurotransmitters.

Neurotransmitter release

The mechanism by which neurotransmitters are dispatched from synaptic vesicles into the synaptic cleft.

Calcium channels in neurons

Specialized ion channels that open in response to electrical signals, facilitating neurotransmitter release.

Synaptic vesicles docking mechanism

The series of interactions and conformations that allow vesicles to attach to the presynaptic membrane.

RRP (readily releasable pool)

The pool of primed synaptic vesicles that are immediately available for release.

Betz et al. 1997

A reference indicating the study that discusses UNC-13 and its role in synaptic function.

Biochemical signals for vesicle fusion

Chemical cues like calcium that facilitate the interaction of proteins required for vesicle release.

Calcium-mediated synaptic activity

The dependence of neurotransmitter release on calcium ion concentration changes.

Vesicle fusion kinetics

The timing and rate at which vesicles fuse with the presynaptic membrane.

High-resolution imaging

Techniques that allow detailed observation of molecular arrangements at synapses.

Calcium-binding proteins

Proteins that alter their configuration or activity in response to calcium ions.

Synaptic physiology

The study of how synaptic transmission occurs and is regulated in the nervous system.

Fusion event

The moment when a vesicle merges with the presynaptic membrane to release its contents.

Synaptic architecture

The structural organization of proteins and membranes at synapses.

SNAP-25

A protein that participates in synaptic vesicle fusion by forming part of the SNARE complex.

Synaptobrevin

Also known as VAMP, a protein involved in vesicle fusion and SNARE complex formation.

Syntaxin

A t-SNARE protein that plays a crucial role in the docking of synaptic vesicles.

Primed vesicles

Vesicles that are prepared for fusion and release at the synapse.

SNARE complex

A protein complex formed between SNAP-25, synaptobrevin, and syntaxin, critical for vesicle fusion.

Fusion competent

The state of vesicles that are ready to fuse with the presynaptic membrane.

Closed syntaxin configuration

A structural state of syntaxin where the SNARE binding domain is hidden, preventing complex formation.

Open syntaxin configuration

The structural state of syntaxin that allows SNARE complex formation.

UNC-13

A protein that binds to the N-terminus of syntaxin and promotes SNARE complex assembly.

Vesicle docking

The process by which synaptic vesicles attach to the presynaptic membrane in preparation for fusion.

Synaptic vesicle (SV)

A small, membrane-bound structure containing neurotransmitters, which is essential for synaptic transmission.

Calcium influx

The entry of calcium ions into the presynaptic terminal, triggering vesicle fusion.

Synaptotagmin I

A calcium-binding protein that regulates vesicle fusion in response to calcium.

Calcium binding

The interaction of calcium ions with proteins that play a role in neurotransmitter release.

DAG

Diacylglycerol, a molecule that regulates transitions in SNARE complex assembly states.

PIP2

Phosphatidylinositol 4,5-bisphosphate, a phospholipid that plays a role in membrane dynamics and protein interactions.

Presynaptic membrane

The membrane of the transmitting neuron where vesicles fuse to release neurotransmitters.

SV docking defects

Issues that arise in the attachment of synaptic vesicles to the presynaptic membrane, leading to impaired neurotransmitter release.

Munc13 ring

A structure that promotes SNARE complex assembly at synapses.

Clamped SNAREpins

State of SNARE complexes where they are held together, awaiting the release triggered by calcium.

Exocytosis

The process by which vesicles release their contents into the extracellular space.

Synchronous release

The coordinated release of neurotransmitters from multiple vesicles in response to an action potential.

High-pressure freezing technique

A method used to preserve synapses in a physiological state for imaging and analysis.

Synaptic cleft

The space between the presynaptic and postsynaptic membranes where neurotransmitters are released.

Calcium-gated channels

Voltage-gated channels that open in response to action potentials, allowing calcium entry.

SNARE zippering

The process by which the SNARE complex tightens, promoting membrane fusion.

C2B domain

A region of synaptotagmin that interacts with the target membrane upon calcium binding.

PM dimple

The inward curve of the plasma membrane caused by synaptotagmin binding.

Action potential

An electrical signal that travels along a neuron, leading to neurotransmitter release.

Primed vesicle state

The condition of vesicles that are ready and waiting at the presynaptic membrane for a calcium signal.

Munc13/UNC-13 interaction

Binding of the Munc13 protein to syntaxin, necessary for vesicle priming.

Synaptic transmission

The process through which signaling is conveyed between neurons via neurotransmitters.

Neurotransmitter release

The mechanism by which neurotransmitters are dispatched from synaptic vesicles into the synaptic cleft.

Calcium channels in neurons

Specialized ion channels that open in response to electrical signals, facilitating neurotransmitter release.

Synaptic vesicles docking mechanism

The series of interactions and conformations that allow vesicles to attach to the presynaptic membrane.

RRP (readily releasable pool)

The pool of primed synaptic vesicles that are immediately available for release.

Betz et al. 1997

A reference indicating the study that discusses UNC-13 and its role in synaptic function.

Biochemical signals for vesicle fusion

Chemical cues like calcium that facilitate the interaction of proteins required for vesicle release.

Calcium-mediated synaptic activity

The dependence of neurotransmitter release on calcium ion concentration changes.

Vesicle fusion kinetics

The timing and rate at which vesicles fuse with the presynaptic membrane.

High-resolution imaging

Techniques that allow detailed observation of molecular arrangements at synapses.

Calcium-binding proteins

Proteins that alter their configuration or activity in response to calcium ions.

Synaptic physiology

The study of how synaptic transmission occurs and is regulated in the nervous system.

Fusion event

The moment when a vesicle merges with the presynaptic membrane to release its contents.

Synaptic architecture

The structural organization of proteins and membranes at synapses.

What is the primary role of Munc13/UNC-13?

It acts as a critical priming factor, opening syntaxin for SNARE complex formation and promoting synaptic vesicle fusion.

Neurotransmitter

Chemical messengers released from synaptic vesicles into the synaptic cleft to transmit signals to other neurons or target cells.

Postsynaptic membrane

The membrane of the neuron or cell receiving the signal, located opposite the presynaptic terminal in a synapse.

Fusion pore

The initial aqueous channel that forms between the synaptic vesicle membrane and the presynaptic membrane during exocytosis, allowing neurotransmitter release.

What initiates the opening of SNAREpins for fusion?

Calcium influx into the presynaptic terminal, leading to synaptotagmin I binding calcium and interacting with the membrane.

N-terminal regulatory domain of Syntaxin

A region in syntaxin that interacts with proteins like Munc13/UNC-13, regulating its transition between closed and open conformations.

What is the sequence of key events from action potential to neurotransmitter release?

Action potential arrival --> Calcium influx --> Vesicle docking & priming --> SNARE complex formation --> Synaptotagmin I-mediated fusion --> Neurotransmitter release into synaptic cleft.

How do SNARE proteins facilitate membrane fusion?

SNARE proteins (SNAP-25, synaptobrevin, syntaxin) form a complex called a SNAREpin that zips together, pulling the vesicle and presynaptic membranes into close apposition, overcoming repulsive forces and initiating fusion.

What is the function of the Readily Releasable Pool (RRP) of synaptic vesicles?

The RRP is the subpopulation of synaptic vesicles that are already docked and primed at the presynaptic membrane, immediately available for rapid, synchronous neurotransmitter release upon calcium influx, ensuring efficient synaptic transmission.

Explain the role of Munc13/UNC-13 in synaptic vesicle priming.

Munc13/UNC-13 binds to the N-terminus of syntaxin, causing it to transition from a closed to an open configuration. This opening is crucial for syntaxin to interact with synaptobrevin and SNAP-25, initiating SNARE complex assembly and thereby priming the vesicle for fusion.