Zaks W J, Creutz C E
Department of Pharmacology, University of Virginia, Charlottesville 22908.
Biochim Biophys Acta. 1990 Nov 2;1029(1):149-60. doi: 10.1016/0005-2736(90)90448-w.
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.
对三种膜联蛋白（突触结合蛋白、p32和p67）的嗜铬粒膜结合和聚集特性进行了研究和比较。每种蛋白质被激活后以双相Ca2+依赖性结合并聚集膜，其中一个阶段在pCa 5.0 - 3.5之间滴定，第二个阶段在较高钙水平（pCa小于3.5）。顺式不饱和游离脂肪酸将这些Ca2+需求降低了约一个对数单位。钡和锶能够部分替代钙，敏感性顺序为Ca2+＞Sr2+＞Ba2+。这些蛋白质似乎与不同但重叠的受体位点群体结合，并且在较高Ca2+水平时以显示正协同性的方式结合。这些蛋白质作为膜聚集剂的最大功效不同，突触结合蛋白比p32有效1 - 2倍，而p32又比p67有效7倍。p67与突触结合蛋白或p32联合时是颗粒聚集的有效抑制剂，而p32能够以随突触结合蛋白浓度变化的方式促进和抑制突触结合蛋白诱导的颗粒聚集。这些膜联蛋白 - 膜相互作用的复杂性可能反映了膜联蛋白的多结构域结构，并且可能对这些蛋白质在细胞中的不同功能有影响。
