title: Single secretory granules of live cells recruit syntaxin-1 and synaptosomal associated protein 25 (SNAP-25) in large copy numbers.
abstract: Before secretory vesicles undergo exocytosis, they must recruit the proteins syntaxin-1 and synaptosomal associated protein 25 (SNAP-25) in the plasma membrane. GFP-labeled versions of both proteins cluster at sites where secretory granules have docked. Single-particle tracking shows that minority populations of both molecules are strongly hindered in their mobility, consistent with their confinement in nanodomains. We measured the fluorescence of granule-associated clusters, the fluorescence of single molecules, and the numbers of unlabeled syntaxin-1 and SNAP-25 molecules per cell. There was a more than 10-fold excess of SNAP-25 over syntaxin-1. Fifty to seventy copies each of syntaxin-1 and SNAP-25 molecules were associated with a single docked granule, many more than have been reported to be required for fusion.
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Knowles
authors.forename: S
authors.initials: S
authors.lastname: Barg
authors.forename: L
authors.initials: L
authors.lastname: Wan
authors.forename: M
authors.initials: M
authors.lastname: Midorikawa
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.forename: Wolfhard
authors.initials: W
authors.lastname: Almers
mesh_terms: D000818:Animals; D002470:Cell Survival; D005453:Fluorescence; D018628:Gene Dosage / Q000235:genetics*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D016716:PC12 Cells; D038761:Photobleaching; D021381:Protein Transport; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000235:genetics / Q000378:metabolism*; D050827:Syntaxin 1 / Q000378:metabolism*
chemical_list: D011993:Recombinant Fusion Proteins; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D049452:Green Fluorescent Proteins