Specific SNARE complex binding mode of the Sec1/Munc-18 protein, Sec1p

Area of Science:

• Cell biology
• Molecular biology
• Biochemistry

Background:

• Sec1/Munc-18 (SM) proteins are essential for vesicle fusion in eukaryotic cells.
• SM proteins interact with soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), potentially activating syntaxin for SNARE complex assembly.
• Yeast Sec1p's lack of binding to yeast plasma-membrane syntaxin Sso1p presents an exception to the general SM-syntaxin binding rule.

Purpose of the Study:

• To investigate the binding interaction between yeast Sec1p and syntaxin Sso1p.
• To determine if a latent binding motif exists in Sso1p that is masked by its closed conformation.
• To elucidate the specific SNARE complex formation required for Sec1p binding and its role in vesicle fusion.

Main Methods:

• Utilized yeast genetics to create and study sso1 mutants.
• Employed in vitro biochemical assays with purified proteins to reconstitute Sec1p binding specificity.
• Analyzed binding affinities of Sec1p to various SNARE complex formations (ternary, binary, individual SNAREs).

Main Results:

• No evidence of a latent binding motif in Sso1p was found, even in mutant forms.
• Sec1p demonstrated specific binding exclusively to the ternary SNARE complex.
• No detectable binding of Sec1p was observed with the binary t-SNARE complex or uncomplexed individual SNARE proteins.

Conclusions:

• The interaction between Sec1p and syntaxin Sso1p does not involve a latent binding motif.
• Vesicle fusion necessitates a specific interaction between SM proteins and the fully assembled ternary SNARE complex.
• This finding refines the understanding of the molecular mechanism underlying SM protein-mediated membrane fusion.