title: Snapin mediates insulin secretory granule docking, but not trans-SNARE complex formation.
abstract: Secretory granule exocytosis is a tightly regulated process requiring granule targeting, tethering, priming, and membrane fusion. At the heart of this process is the SNARE complex, which drives fusion through a coiled-coil zippering effect mediated by the granule v-SNARE protein, VAMP2, and the plasma membrane t-SNAREs, SNAP-25 and syntaxin-1A. Here we demonstrate that in pancreatic β-cells the SNAP-25 accessory protein, snapin, C-terminal H2 domain binds SNAP-25 through its N-terminal Sn-1 domain. Interestingly whilst snapin binds SNAP-25, there is only modest binding of this complex with syntaxin-1A under resting conditions. Instead synataxin-1A appears to be recruited in response to secretory stimulation. These results indicate that snapin plays a role in tethering insulin granules to the plasma membrane through coiled coil interaction of snapin with SNAP-25, with full granule fusion competency only resulting after subsequent syntaxin-1A recruitment triggered by secretory stimulation.
authors.affiliation: Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AT, UK.
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Somanath
authors.affiliation: Diabetes Research Laboratories, Oxford Centre for Diabetes, Endocrinology and Churchill Hospital, University of Oxford, Oxford, OX3 7LJ, UK.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Partridge
authors.affiliation: Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, E1 2AT, UK.
authors.forename: Catriona
authors.initials: C
authors.lastname: Marshall
authors.affiliation: CSL Limited, 45 Poplar Road, Parkville, Victoria 3052, Australia.
authors.forename: Tony
authors.initials: T
authors.lastname: Rowe
authors.affiliation: Interdisciplinary Biomedical Research Centre, School of Science and Technology, Nottingham Trent University, Nottingham, NG11 8NS, UK. Electronic address: mark.turner@ntu.ac.uk.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Turner
mesh_terms: D000818:Animals; D002460:Cell Line; D005089:Exocytosis; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000032:analysis / Q000378:metabolism*; D050827:Syntaxin 1 / Q000032:analysis / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000032:analysis / Q000378:metabolism*
chemical_list: D007328:Insulin; D050600:SNARE Proteins; C494210:Snap25 protein, rat; C498452:Snapin protein, rat; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins
keywords: Exocytosis; SNAP-25; Secretory granule tethering