title: Annexin-chromaffin granule membrane interactions: a comparative study of synexin, p32 and p67.
abstract: The chromaffin granule membrane binding and aggregating properties of three annexins, synexin, p32 and p67, have been studied and compared. Each protein was activated to bind and aggregate membranes with a biphasic Ca2+ dependence, with one phase titrating between pCa 5.0-3.5 and the second at higher levels of calcium (pCa less than 3.5). cis-Unsaturated free fatty acids lowered these Ca2+ requirements by approximately one log unit. Barium and strontium were able to partially substitute for calcium, with the order of sensitivity Ca2+ greater than Sr2+ greater than Ba2+. The proteins appeared to bind to distinct but overlapping populations of receptor sites, and did so in a manner displaying positive cooperativity at the higher Ca2+ levels. The maximal efficacy of the proteins as membrane aggregators differed with synexin being 1-2-fold more efficacious than p32, which in turn was 7-fold more efficacious than p67. In combination, p67 was an effective inhibitor of granule aggregation induced by synexin or p32, while p32 was able to both promote and inhibit synexin-induced granule aggregation in a manner which varied with synexin concentration. The complexity of these annexin-membrane interactions may be a reflection of the multidomain structure of the annexins and may have implications for the differential functions of these proteins in cells.
authors.affiliation: Department of Pharmacology, University of Virginia, Charlottesville 22908.
authors.forename: W J
authors.initials: WJ
authors.lastname: Zaks
authors.forename: C E
authors.initials: CE
authors.lastname: Creutz
mesh_terms: D000818:Animals; D017310:Annexin A7; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002837:Chromaffin Granules / Q000187:drug effects / Q000378:metabolism*; D005227:Fatty Acids / Q000494:pharmacology; D008099:Liver / Q000737:chemistry; D011506:Proteins / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D038981:Receptors, Collagen
chemical_list: D017310:Annexin A7; D002135:Calcium-Binding Proteins; D005227:Fatty Acids; D011506:Proteins; D011956:Receptors, Cell Surface; D038981:Receptors, Collagen; D002118:Calcium