title: Amisyn, a novel syntaxin-binding protein that may regulate SNARE complex assembly.
abstract: The regulation of SNARE complex assembly likely plays an important role in governing the specificity as well as the timing of membrane fusion. Here we identify a novel brain-enriched protein, amisyn, with a tomosyn- and VAMP-like coiled-coil-forming domain that binds specifically to syntaxin 1a and syntaxin 4 both in vitro and in vivo, as assessed by co-immunoprecipitation from rat brain. Amisyn is mostly cytosolic, but a fraction co-sediments with membranes. The amisyn coil domain can form SNARE complexes of greater thermostability than can VAMP2 with syntaxin 1a and SNAP-25 in vitro, but it lacks a transmembrane anchor and so cannot act as a v-SNARE in this complex. The amisyn coil domain prevents the SNAP-25 C-terminally mediated rescue of botulinum neurotoxin E inhibition of norepinephrine exocytosis in permeabilized PC12 cells to a greater extent than it prevents the regular exocytosis of these vesicles. We propose that amisyn forms nonfusogenic complexes with syntaxin 1a and SNAP-25, holding them in a conformation ready for VAMP2 to replace it to mediate the membrane fusion event, thereby contributing to the regulation of SNARE complex formation.
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305-5345, USA.
authors.forename: Suzie J
authors.initials: SJ
authors.lastname: Scales
authors.forename: Boris A
authors.initials: BA
authors.lastname: Hesser
authors.forename: Esteban S
authors.initials: ES
authors.lastname: Masuda
authors.forename: Richard H
authors.initials: RH
authors.lastname: Scheller
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D005089:Exocytosis; D005982:Glutathione Transferase / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000378:metabolism; D016716:PC12 Cells; D010673:Pheochromocytoma; D017433:Protein Structure, Secondary; D050765:Qa-SNARE Proteins; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D050600:SNARE Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D013816:Thermodynamics; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D011993:Recombinant Fusion Proteins; C494208:SNAP25 protein, human; D050600:SNARE Proteins; C494212:STX1A protein, human; C465215:STXBP6 protein, human; C494210:Snap25 protein, rat; C494213:Stx1a protein, rat; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins; D005982:Glutathione Transferase; D009638:Norepinephrine