Rab3a binding and secretion-enhancing domains in Rim1 are separate and unique. Studies in adrenal chromaffin cells.
Rim1 was identified in brain by its ability to bind Rab3a-GTP and has been postulated to be a Rab3a effector protein. Like Rabphilin3, it modulates secretion and contains a zinc finger and two C2 domains. We have investigated the structural basis for the ability of Rim1 to bind Rab3a-GTP and to stimulate exocytosis in chromaffin cells. Both full-length and N-terminal Rim1 enhance secretion 40-50% in both intact and permeabilized cells. The abilities of Rim1 to enhance secretion and to bind Rab3a-GTP reside on distinct and relatively small domains that act independently. A approximately 30-amino acid sequence immediately N-terminal of the zinc finger constitutes the minimal Rab3a-GTP binding domain. This short sequence is not found in Rabphilin3 and is entirely different from the zinc finger and flanking regions of Rabphilin3 that bind Rab3a-GTP. The zinc finger domain in Rim1 is unnecessary for Rab3a-GTP binding but, alone, enhances secretion. An analysis of the characteristics of the enhancement of secretion in permeabilized chromaffin cells indicates that N-terminal Rim1 does not alter the sensitivity of secretion to Ca(2+) but, instead, increases the rate of ATP-dependent priming of secretion.
Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0632, USA.
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Holz
D048868:Adaptor Proteins, Signal Transducing; D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism*; D019204:GTP-Binding Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D016296:Mutagenesis; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D014162:Transfection; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D020826:rab3A GTP-Binding Protein / Q000378:metabolism*; D000097624:Rabphilin-3A
D048868:Adaptor Proteins, Signal Transducing; D019204:GTP-Binding Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins; D020826:rab3A GTP-Binding Protein; D000097624:Rabphilin-3A; C491492:RIMS1 protein, human; C107293:Rim protein, mammalian