title: Regulation of the GTPase cycle of the neuronally expressed Ras-like GTP-binding protein Rab3A.
abstract: The small GTP-binding protein Rab3A (identical to smg p25A) is expressed in neural/exocrine/endocrine cells, is distributed between the cytosol and secretory vesicle membranes, and may cycle between these locations to regulate exocytosis. It is proposed that the GTP/GDP state of Rab3A controls this distribution. In PC12 cells, cytosolic Rab3A is predominantly GDP-bound, whereas membrane-associated Rab3A is approximately 50% GTP-bound. Two cytosolic factors, GDP dissociation inhibitor (GDI) and guanine nucleotide releasing factor (GRF), act only on GDP.Rab3A, and preferentially with post-translationally modified Rab3A. Rab3A GTPase-activating protein (GAP) does not preferentially act on processed Rab3A, and interacts selectively with GTP.Rab3A. GDI antagonizes GRF but not GAP activity toward Rab3A. These data are consistent with the concept of an ordered Rab3A cycle controlled by factors that regulate the guanine-nucleotide binding state of Rab3A.
authors.affiliation: Department of Psychiatry, University of Vermont, Burlington 05405.
authors.forename: E S
authors.initials: ES
authors.lastname: Burstein
authors.forename: W H
authors.initials: WH
authors.lastname: Brondyk
authors.forename: I G
authors.initials: IG
authors.lastname: Macara
authors.forename: K
authors.initials: K
authors.lastname: Kaibuchi
authors.forename: Y
authors.initials: Y
authors.lastname: Takai
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D020730:Guanine Nucleotide Dissociation Inhibitors; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D009474:Neurons / Q000378:metabolism*; D016716:PC12 Cells; D011499:Protein Processing, Post-Translational; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism; D020692:rab3 GTP-Binding Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
chemical_list: D020730:Guanine Nucleotide Dissociation Inhibitors; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins