Newbell B J, Anderson J T, Jarrett H W
Department of Biochemistry, University of Tennessee, Memphis 38163, USA.
Biochemistry. 1997 Feb 11;36(6):1295-305. doi: 10.1021/bi962452n.
Syntrophins are peripheral membrane proteins which have been found associated with dystrophin, the protein product of the Duchenne muscular dystrophy gene locus. Mouse alpha1 syntrophin binds the COOH-terminal domain of dystrophin, and calmodulin inhibits this interaction in a Ca2+-dependent fashion. Where calmodulin binds to syntrophin was investigated by constructing fusion proteins containing different regions of syntrophin's sequence. Syntrophin contains at least two regions which bind calmodulin in different ways. The COOH-terminal 24 residues contain a Ca2+-calmodulin binding site, named CBS-C, which binds calmodulin with an apparent affinity of 18 nM and which is highly conserved in all syntrophins. The amino-terminal 174 residue section of syntrophin contains other calmodulin binding, and binding occurs in either the presence or absence of Ca2+ with an apparent affinity of 100 nM. Syntrophin was shown to bind Ca2+ at two or more sites residing in the amino-terminal 274 residues, and Ca2+ binding to syntrophin affects calmodulin binding at high concentrations of syntrophin. Syntrophin A (residues 4-274) is predominantly a dimer in EGTA. A model of syntrophin's complex interactions with itself (i.e., oligomerization), calmodulin, and Ca2+ is presented.
肌养蛋白是外周膜蛋白，已发现其与杜兴氏肌营养不良基因位点的蛋白产物肌营养不良蛋白相关。小鼠α1肌养蛋白与肌营养不良蛋白的COOH末端结构域结合，而钙调蛋白以Ca2+依赖的方式抑制这种相互作用。通过构建包含肌养蛋白序列不同区域的融合蛋白，研究了钙调蛋白与肌养蛋白的结合位点。肌养蛋白至少有两个以不同方式结合钙调蛋白的区域。COOH末端的24个残基包含一个Ca2+ - 钙调蛋白结合位点，称为CBS - C，其与钙调蛋白的表观亲和力为18 nM，并且在所有肌养蛋白中高度保守。肌养蛋白的氨基末端174个残基部分包含其他钙调蛋白结合位点，无论有无Ca2+ 均会发生结合，表观亲和力为100 nM。已证明肌养蛋白在氨基末端274个残基中的两个或更多位点结合Ca2+ ，并且在高浓度肌养蛋白时，Ca2+ 与肌养蛋白的结合会影响钙调蛋白的结合。肌养蛋白A（残基4 - 274）在EGTA中主要是二聚体。本文提出了肌养蛋白与自身（即寡聚化）、钙调蛋白和Ca2+ 复杂相互作用的模型。
