Lipid bilayer fusion is mediated by SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) located on the vesicle membrane (v-SNAREs) and the target membrane (t-SNAREs)1,2. The assembled v-SNARE/t-SNARE complex consists of a bundle of four helices, of which one is supplied by the v-SNARE and the other three by the t-SNARE3. For t-SNAREs on the plasma membrane, the protein syntaxin4 supplies one helix and a SNAP-25 protein5 contributes the other two. Although there are numerous homologues of syntaxin on intracellular membranes6, there are only two SNAP-25-related proteins in yeast, Sec9 and Spo20, both of which are localized to the plasma membrane and function in secretion7 and sporulation8, respectively. What replaces SNAP-25 in t-SNAREs of intracellular membranes? Here we show that an intracellular t-SNARE is built from a ‘heavy chain’ homologous to syntaxin and two separate non-syntaxin ‘light chains’. SNAP-25 may thus be the exception rather than the rule, having been derived from genes that encoded separate light chains that fused during evolution to produce a single gene encoding one protein with two helices.
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We wish to thank B. Brügger for preparation of the vacuolar lipid mixture and T. Wolfe for help with the manuscript. This work was supported by an NIH grant (to J.E.R.) and postdoctoral fellowships of the Japan Society for the Promotion of Science (to R.F.), the Human Frontiers Science Program Organization (to W.N.), the Deutsche Forschungsgemeinschaft (to T.E.), the Medical Research Council of Canada (to F.P.), the National Institutes of Health (to J.A.M.), the Swiss National Science Foundation (to T.W.) and the European Molecular Biology Organization (to T.W.).
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Fukuda, R., McNew, J., Weber, T. et al. Functional architecture of an intracellular membrane t-SNARE. Nature 407, 198–202 (2000) doi:10.1038/35025084
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