title: Novel Ca2+-binding protein (CAPS) related to UNC-31 required for Ca2+-activated exocytosis.
abstract: Exocytotic secretion in neuroendocrine cells is activated by cytoplasmic Ca2+ increases. Late post-docking events in dense core vesicle exocytosis in permeable PC12 cells require cytosolic factors for sequential ATP-dependent priming and Ca2+-dependent triggering steps. The cytosolic proteins phosphatidylinositol transfer protein and phosphatidylinositol (4)-phosphate 5-kinase, as well as membrane-bound N-ethylmaleimide-sensitive factor, are required for the ATP-dependent priming step. Following priming, the Ca2+-dependent triggering of vesicle fusion requires an additional cytosolic factor, CAPS, which was purified as a 145-kDa protein. To clarify late Ca2+-dependent events in vesicle fusion, the sequence of rat CAPS cDNA was determined and found to encode a novel protein that is the vertebrate homologue of the Caenorhabditis elegans UNC-31 protein shown genetically to be required for neurosecretion. Recombinant CAPS substituted for cytosol in the Ca2+ triggering step in permeable PC12 cells and exhibited moderate affinity (Kd = 270 microM) Ca2+ binding (2 mol Ca2+/mol CAPS dimer), consistent with a role at a Ca2+-regulated step in exocytosis.
authors.affiliation: Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: K
authors.initials: K
authors.lastname: Ann
authors.forename: J A
authors.initials: JA
authors.lastname: Kowalchyk
authors.forename: K M
authors.initials: KM
authors.lastname: Loyet
authors.forename: T F
authors.initials: TF
authors.lastname: Martin
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D005089:Exocytosis; D015801:Helminth Proteins / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016716:PC12 Cells; D049294:Phospholipid Transfer Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D051381:Rats
chemical_list: C485812:Cadps protein, rat; D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D015801:Helminth Proteins; D008565:Membrane Proteins; D049294:Phospholipid Transfer Proteins; C107581:UNC-31 protein, C elegans; D000255:Adenosine Triphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D002118:Calcium