Labbé J P, Boyer M, Roustan C, Benyamin Y
Centre de Recherches de Biochimie Macromoléculaire U.P.R. (C.N.R.S.), Unité 249 (I.N.S.E.R.M.), Montpellier, France.
Biochem J. 1992 May 15;284 ( Pt 1)(Pt 1):75-9. doi: 10.1042/bj2840075.
The actin-myosin head complex in the rigor state reveals several high-affinity sites on the actin molecule in sequences 18-28 and 40-113. In the presence of Mg(2+)-ATP, participation of the actin N-terminal 1-7 sequence is known to occur. The proximity of the C-terminal region of actin to the A1 light chain of the myosin head [S-1(A1)] (where S-1 is myosin subfragment-1) was described previously. We observed that C-terminal antigenic structures located near Met-305, Met-325 and Met-355 and the C-terminal end (Cys-374) of actin are markedly modified in the presence of S-1(A1), S-1(A2) and scallop S-1 and in the absence of Mg(2+)-ATP. This seems to rule out any important specific involvement of the A1 light chain in the described conformational changes. An S-1-binding site was located in this actin C-terminal region by testing the tryptic CB9 peptide (360-372 sequence) previously implicated in the A1 light chain interaction. This peptide was able to bind well to S-1(A1), S-1(A2) and scallop S-1, but not in the presence of Mg(2+)-pyrophosphate. These results strengthen the hypothesis of a multisite interface between S-1 and actin located in the actin subdomain I.
处于僵直状态的肌动蛋白-肌球蛋白头部复合物在肌动蛋白分子的18-28和40-113序列中显示出几个高亲和力位点。已知在Mg(2+)-ATP存在的情况下，肌动蛋白N端1-7序列会参与其中。先前已描述了肌动蛋白C端区域与肌球蛋白头部的A1轻链[S-1(A1)]（其中S-1是肌球蛋白亚片段-1）的接近程度。我们观察到，在存在S-1(A1)、S-1(A2)和扇贝S-1且不存在Mg(2+)-ATP的情况下，位于肌动蛋白Met-305、Met-325和Met-355附近的C端抗原结构以及肌动蛋白的C端（Cys-374）会发生明显改变。这似乎排除了A1轻链在所述构象变化中任何重要的特异性参与。通过测试先前涉及A1轻链相互作用的胰蛋白酶CB9肽（360-372序列），在该肌动蛋白C端区域定位了一个S-1结合位点。该肽能够与S-1(A1)、S-1(A2)和扇贝S-1很好地结合，但在存在Mg(2+)-焦磷酸的情况下则不能。这些结果强化了位于肌动蛋白亚结构域I中的S-1与肌动蛋白之间存在多位点界面的假设。
