Selective formation of Sed5p-containing SNARE complexes is mediated by combinatorial binding interactions.
Sed5p is the only syntaxin family member required for protein transport through the yeast Golgi and it is known to bind up to nine other soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins in vivo. We describe in vitro binding experiments in which we identify ternary and quaternary Sed5p-containing SNARE complexes. The formation of SNARE complexes among these endoplasmic reticulum- and Golgi-localized proteins requires Sed5p and is syntaxin-selective. In addition, Sed5p-containing SNARE complexes form selectively and this selectivity is mediated by Sed5p-containing intermediates that discriminate among subsequent binding partners. Although many of these SNAREs have overlapping distributions in vivo, the SNAREs that form complexes with Sed5p in vitro reflect their functionally distinct locales. Although SNARE-SNARE interactions are promiscuous and a single SNARE protein is often found in more than one complex, both the biochemical as well as genetic analyses reported here suggest that this is not a result of nonselective direct substitution of one SNARE for another. Rather our data are consistent with the existence of multiple (perhaps parallel) trafficking pathways where Sed5p-containing SNARE complexes play overlapping and/or distinct functional roles.
Department of Biology, The Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China.
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Tsui
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Tai
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Banfield
D000595:Amino Acid Sequence; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D005656:Fungal Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; C083242:SNC2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C077554:Sed5 protein, S cerevisiae; C106736:VTI1 protein, S cerevisiae; D033921:Vesicular Transport Proteins