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首页> 外文期刊>Biochemistry >Addition of Lysines to the 50/20 kDa Junction of Myosin Strengthens Weak Binding to Actin without Affecting the Maximum ATPase Activity.
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Addition of Lysines to the 50/20 kDa Junction of Myosin Strengthens Weak Binding to Actin without Affecting the Maximum ATPase Activity.

机译：在肌球蛋白的50/20 kDa连接处添加赖氨酸可增强与肌动蛋白的弱结合，而不会影响最大ATPase活性。

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摘要

Much interest has centered on two surface loops in the motor domain to explain the differences in enzymatic and mechanical properties of myosin isoforms. We showed that two invariant lysines at the C-terminal end of loop 2, which is part of the actin-binding interface, are required to obtain actin activation [Joel et al. (2001) J. Biol. Chem. 276, 2998-3003]. Here we investigate the effects of increasing positive charge in the variable portion of loop 2 of smooth muscle heavy meromyosin (smHMM). Increasing the net positive charge by +4 increased the affinity for actin in the presence and absence of ATP. The K(m) for actin-activated ATPase activity decreased 15-fold, but V(max) was unchanged, showing that weak binding without increasing the rate-limiting step for V(max). The mutant HMM had slower rates of in vitro motility and ADP release compared to WT HMM. ADP release and motility, which were both salt-dependent, correlated linearly with each other. Loop 2 thus plays a major role in setting the affinity for actin but also affects ADP release and motility. Because the actin- and nucleotide-binding regions communicate, mutations to one region can impact multiple facets of myosin's mechanical and enzymatic properties.
机译：许多兴趣都集中在运动域中的两个表面环上，以解释肌球蛋白同工型在酶和机械性质方面的差异。我们发现在环2的C末端有两个不变的赖氨酸，这是肌动蛋白结合界面的一部分，是获得肌动蛋白激活所必需的[Joel等。 （2001）J.Biol。化学276，2998-3003]。在这里，我们研究了平滑肌重肌球蛋白（smHMM）2环可变部分中正电荷增加的影响。在存在和不存在ATP的情况下，将净正电荷增加+4会增加对肌动蛋白的亲和力。肌动蛋白激活ATPase活性的K（m）降低15倍，但V（max）不变，表明弱结合而没有增加V（max）的限速步骤。与野生型HMM相比，突变型HMM具有较低的体外运动和ADP释放速率。 ADP的释放和运动性都与盐有关，两者之间呈线性相关。因此，环2在设定对肌动蛋白的亲和力中起主要作用，但也影响ADP的释放和运动性。因为肌动蛋白和核苷酸的结合区域相互连通，所以一个区域的突变会影响肌球蛋白的机械和酶促特性的多个方面。

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