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Modulation of actin affinity and actomyosin adenosine triphosphatase by charge changes in the myosin motor domain

机译：肌球蛋白运动域中电荷的变化对肌动蛋白亲和力和肌动球蛋白腺苷三磷酸酶的调节

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摘要

The effects of mutations in an actin-binding surface loop of myosin (loop 2) are described. Part of loop 2, the segment between myosin residues 618 and 622, was replaced with sequences enlarged by the introduction of positively charged GKK or neutral GNN motifs. Constructs with loops carrying up to 20 additional amino acids and charge variations from -1 to +12 were produced. Steady-state and transient kinetics were used to characterize the enzymatic behavior of the mutant motor domains. Binding of nucleotide was not affected by any of the alterations in loop 2. In regard to their interaction with actin, constructs with moderate charge changes (-1 to +2) displayed wild-type-like behavior. Introduction of more than one GKK motif led to stronger coupling between the actin-and nucleotide-binding sites of myosin and an up to 1000-fold increased affinity for actin in the absence of ATP and at zero ionic strength, In comparison to the wild-type construct M765, constructs with 4-12 extra charges displayed an increased dependence on ionic strength in their interaction with actin, a 2-3-fold increase in k(cat), a more than 10-fold reduction in K-app for actin, and a 34-70-fold increase in catalytic efficiency. [References: 42]
机译：描述了肌球蛋白的肌动蛋白结合表面环（环2）中突变的影响。环2的一部分，肌球蛋白残基618和622之间的区段，被引入带正电荷的GKK或中性GNN基序扩大的序列所取代。产生了带有环的构建体，所述环携带多达20个其他氨基酸并且电荷在-1至+12之间变化。稳态和瞬态动力学用来表征突变体运动域的酶促行为。核苷酸的结合不受环2中任何变化的影响。关于它们与肌动蛋白的相互作用，具有中等电荷变化（-1至+2）的构建体显示出野生型样的行为。与野生型相比，引入多个GKK基序可导致肌球蛋白的肌动蛋白和核苷酸结合位点之间更强的偶联，并且在不存在ATP且离子强度为零的情况下，对肌动蛋白的亲和力最多提高1000倍。 M765型构建体，具有4-12个额外电荷的构建体在与肌动蛋白的相互作用中显示出对离子强度的依赖性增加，k（cat）升高2-3倍，肌动蛋白的K-app降低10倍以上，催化效率提高了34-70倍。 [参考：42]

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