title: Rab1 and Ca2+ are required for the fusion of carrier vesicles mediating endoplasmic reticulum to Golgi transport.
abstract: Members of the rab/YPT1/SEC4 gene family of small molecular weight GTPases play key roles in the regulation of vesicular traffic between compartments of the exocytic pathway. Using immunoelectron microscopy, we demonstrate that a dominant negative rab1a mutant, rab1a(N124I), defective for guanine nucleotide binding in vitro, leads to the accumulation of vesicular stomatitis virus glycoprotein (VSV-G) in numerous pre-cis-Golgi vesicles and vesicular-tubular clusters containing rab1 and beta-COP, a subunit of the coatomer complex. Similar to previous observations (Balch et al. 1994. Cell. 76:841-852), VSV-G was concentrated nearly 5-10-fold in vesicular carriers that accumulate in the presence of the rab1a(N124I) mutant. VSV-G containing vesicles and vesicular-tubular clusters were also found to accumulate in the presence of a rab1a effector domain peptide mimetic that inhibits endoplasmic reticulum to Golgi transport, as well as in the absence of Ca2+. These results suggest that the combined action of a Ca(2+)-dependent protein and conformational changes associated with the GTPase cycle of rab1 are essential for a late targeting/fusion step controlling the delivery of vesicles to Golgi compartments.
authors.affiliation: Department of Cell Biology, Scripps Research Institute, La Jolla, California 92037.
authors.forename: S N
authors.initials: SN
authors.lastname: Pind
authors.forename: C
authors.initials: C
authors.lastname: Nuoffer
authors.forename: J M
authors.initials: JM
authors.lastname: McCaffery
authors.forename: H
authors.initials: H
authors.lastname: Plutner
authors.forename: H W
authors.initials: HW
authors.lastname: Davidson
authors.forename: M G
authors.initials: MG
authors.lastname: Farquhar
authors.forename: W E
authors.initials: WE
authors.lastname: Balch
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002213:Capsid / Q000378:metabolism; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008562:Membrane Glycoproteins; D016253:Microscopy, Immunoelectron; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D014759:Viral Envelope Proteins / Q000378:metabolism; D020761:rab1 GTP-Binding Proteins
chemical_list: C028391:G protein, vesicular stomatitis virus; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D014759:Viral Envelope Proteins; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D020761:rab1 GTP-Binding Proteins; D002118:Calcium