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首页> 外文期刊>Biochemistry >Two-Headed Binding of the Unphosphorylated Nonmuscle Heavy Meromyosin centre dot ADP Complex to Actin
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Two-Headed Binding of the Unphosphorylated Nonmuscle Heavy Meromyosin centre dot ADP Complex to Actin

机译：未磷酸化的非肌肉重肌球蛋白中心点ADP复合物与肌动蛋白的双头结合。

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The enzymatic and motor function of smooth muscle and nonmuscle myosin II is activated by phosphorylation of the regulatory light chains located in the head portion of myosin.Dimerization of the heads,which is brought about by the coiled-coil tail region,is essential for regulation since single-headed fragments are active regardless of the state of phosphorylation.Utilizing the fluorescence signal on binding of myosin to pyrene-labeled actin filaments,we investigated the interplay of actin and nucleotide binding to thiophosphorylated and unphosphorylated recombinant nonmuscle IIA heavy meromyosin constructs.We show that both heads of either thiophosphorylated or unphosphorylated heavy meromyosin bind very strongly to actin(K_d<10 nM)in the presence or absence of ADP.The heads have high and indistinguishable affinities for ADP(K_d around 1 muM)when bound to actin.These findings are in line with the previously observed unusually loose coupling between nucleotide and actin binding to nonmuscle myosin IIA subfragment-1(Kovacs et al.(2003)J.Biol.Chem.278,38132.).Furthermore,they imply that the structure of the two heads in the ternary actomyosin-ADP complex is symmetrical and that the asymmetrical structure observed in the presence of ATP and the absence of actin in previous investigations(Wendt et al.(2001)Proc.Natl.Acad.Sci.U.S.A.98,4361)is likely to represent an ATPase intermediate that precedes the actomyosin-ADP state.
机译：平滑肌和非肌肉肌球蛋白II的酶促和运动功能通过位于肌球蛋白头部的调节性轻链的磷酸化而激活。由盘绕线圈尾部区域引起的头的二聚化对于调节至关重要由于单头片段无论磷酸化状态如何均具有活性。利用荧光信号对肌球蛋白与pyr标记的肌动蛋白丝的结合进行研究，我们研究了肌动蛋白的相互作用以及核苷酸与硫代磷酸化和非磷酸化重组非肌肉IIA重度肌球蛋白构建体的结合。表明在存在或不存在ADP的情况下，硫代磷酸化或未磷酸化的重肌球蛋白的两个头部都非常强烈地与肌动蛋白（K_d <10 nM）紧密结合。当与肌动蛋白结合时，这些头部对ADP（K_d的亲和力约为1μM）具有高且不可区分的亲和力。这些发现与先前观察到的核苷酸和肌动蛋白与nonm的结合之间异常松散的偶联一致肌球蛋白IIA亚片段1（Kovacs等人（2003）J.Biol.Chem.278,38132。）。此外，它们暗示三元放线菌素ADP复合物中两个头的结构是对称的，并且不对称在先前的研究中（Wendt et al。（2001）Proc.Natl.Acad.Sci.USA98,4361）在存在ATP和不存在肌动蛋白的情况下观察到的结构可能代表了在放线菌素-ADP状态之前的ATPase中间体。

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