Velaz L, Chen Y D, Chalovich J M
Department of Biochemistry, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354.
Biophys J. 1993 Aug;65(2):892-8. doi: 10.1016/S0006-3495(93)81113-5.
The protein caldesmon inhibits actin-activated ATP hydrolysis of myosin and inhibits the binding of myosin.ATP to actin. A fragment isolated from a chymotryptic digest of caldesmon contains features of the intact molecule that make it useful as a selective inhibitor of the binding of myosin.ATP complexes to actin without having the complexity of binding to myosin. The COOH-terminal 20 kDa region of caldesmon binds to actin with one-sixth the affinity of caldesmon with a stoichiometry of binding of one fragment per two actin monomers. This contrasts with the 1:6-9 stoichiometry of intact caldesmon. The binding of the 20 kDa fragments to actin is totally reversed by Ca(2+)-calmodulin and, like intact caldesmon, the 20 kDa fragments are competitive with the binding of myosin subfragments to actin. This competition with myosin binding is largely responsible for the inhibition of ATP hydrolysis, although both the fragments and intact caldesmon also reverse the potentiation of ATPase activity caused by tropomyosin. These polypeptides are useful both in defining the function of caldesmon and in studying the role of weakly bound cross-bridges in muscle.
钙调蛋白可抑制肌动蛋白激活的肌球蛋白ATP水解，并抑制肌球蛋白-ATP与肌动蛋白的结合。从钙调蛋白的胰凝乳蛋白酶消化物中分离出的一个片段具有完整分子的特征，使其成为一种有用的选择性抑制剂，可抑制肌球蛋白-ATP复合物与肌动蛋白的结合，而不会出现与肌球蛋白结合的复杂性。钙调蛋白的COOH末端20 kDa区域与肌动蛋白的结合亲和力是钙调蛋白的六分之一，每两个肌动蛋白单体结合一个片段的化学计量比。这与完整钙调蛋白1:6 - 9的化学计量比形成对比。20 kDa片段与肌动蛋白的结合可被Ca(2 +)-钙调蛋白完全逆转，并且与完整的钙调蛋白一样，20 kDa片段与肌球蛋白亚片段与肌动蛋白的结合具有竞争性。与肌球蛋白结合的这种竞争在很大程度上导致了ATP水解的抑制，尽管片段和完整的钙调蛋白也能逆转原肌球蛋白引起的ATP酶活性增强。这些多肽在确定钙调蛋白的功能以及研究弱结合交叉桥在肌肉中的作用方面都很有用。
