A half-zippered SNARE complex represents a functional intermediate in membrane fusion.

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins are essential for membrane fusion.
• SNAREs mediate membrane fusion through a zippering mechanism, assembling from N-termini to C-termini.
• Previous studies suggest multi-stage assembly of SNARE complexes.

Purpose of the Study:

• To elucidate the functional, sequential steps of SNARE protein assembly during membrane fusion.
• To define the specific roles of different SNARE domains in the fusion process.
• To investigate the rate-limiting step in SNARE-mediated membrane fusion.

Main Methods:

• Biophysical analysis of SNARE protein interactions.
• Characterization of conformational changes during SNARE complex assembly.
• Functional assays to determine the necessity and sufficiency of different assembly steps for membrane fusion.

Main Results:

• Membrane fusion requires a sequential, two-step SNARE folding pathway.
• The N-terminal domain (NTD) of v-SNARE docks to t-SNARE, forming a half-zippered complex and creating a binding site for v-SNARE's C-terminal domain (CTD).
• Subsequent zippering of CTD, linker (LD), and transmembrane (TMD) domains triggers fusion; NTD assembly is the rate-limiting step.

Conclusions:

• SNARE-mediated membrane fusion proceeds via a defined two-step mechanism.
• Distinct functional roles are assigned to the N-terminal and C-terminal assembly stages.
• This framework explains the action of regulators like complexin and refines understanding of SNARE function.