title: Fusogenic pairings of vesicle-associated membrane proteins (VAMPs) and plasma membrane t-SNAREs--VAMP5 as the exception.
abstract: BACKGROUND
  Intracellular vesicle fusion is mediated by the interactions of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins on vesicles (v-SNAREs) and on target membranes (t-SNAREs). The vesicle-associated membrane proteins (VAMPs) are v-SNAREs that reside in various post-Golgi vesicular compartments. To fully understand the specific role of each VAMP in vesicle trafficking, it is important to determine if VAMPs have differential membrane fusion activities.
  
  
  RESULTS
  In this study, we developed a cell fusion assay that quantifies SNARE-mediated membrane fusion events by activated expression of β-galactosidase, and examined fusogenic pairings between the seven VAMPs, i.e., VAMPs 1, 2, 3, 4, 5, 7 and 8, and two plasma membrane t-SNARE complexes, syntaxin1/SNAP-25 and syntaxin4/SNAP-25. VAMPs 1, 2, 3, 4, 7 and 8 drove fusion efficiently, whereas VAMP5 was unable to mediate fusion with the t-SNAREs. By expressing VAMPs 1, 3, 4, 7 and 8 at the same level, we further compared their membrane fusion activities. VAMPs 1 and 3 had comparable and the highest fusion activities, whereas VAMPs 4, 7 and 8 exhibited 30-50% lower fusion activities. Moreover, we determined the dependence of cell fusion activity on VAMP1 expression level. Analysis of the dependence data suggested that there was no cooperativity of VAMP proteins in the cell fusion reaction.
  
  
  CONCLUSIONS
  These data indicate that VAMPs have differential membrane fusion capacities, and imply that with the exception of VAMP5, VAMPs are essentially redundant in mediating fusion with plasma membrane t-SNAREs.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, Louisville, Kentucky, United States of America.
authors.forename: Nazarul
authors.initials: N
authors.lastname: Hasan
authors.forename: Deborah
authors.initials: D
authors.lastname: Corbin
authors.forename: Chuan
authors.initials: C
authors.lastname: Hu
mesh_terms: D000818:Animals; D019556:COS Cells; D002459:Cell Fusion; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D042783:Endothelial Cells / Q000166:cytology; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D007763:Lac Operon; D008565:Membrane Proteins / Q000378:metabolism; D050683:R-SNARE Proteins / Q000378:metabolism*; D050600:SNARE Proteins / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; C476456:VAMP4 protein, human; C485545:VAMP5 protein, human