Amisyn, a novel syntaxin-binding protein that may regulate SNARE complex assembly.
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.
Scales
Suzie J
SJ
Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305-5345, USA.
Hesser
Boris A
BA
Masuda
Esteban S
ES
Scheller
Richard H
RH
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
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