Canepari M, Rossi R, Pellegrino M A, Bottinelli R, Schiaffino S, Reggiani C
Institute of Human Physiology, University of Pavia, Italy.
J Muscle Res Cell Motil. 2000 May;21(4):375-82. doi: 10.1023/a:1005640004495.
To define the structural differences that are responsible for the functional diversity between orthologous sarcomeric myosins, we compared the rat and human beta/slow myosins. Functional comparison showed that rat beta/slow myosin has higher ATPase activity and moves actin filaments at higher speed in in vitro motility assay than human beta/slow myosin. Sequence analysis shows that the loop regions at the junctions of the 25 and 50 kDa domains (loop 1) and the 50 and 20 kDa domains (loop 2), which have been implicated in determining functional diversity of myosin heavy chains, are essentially identical in the two orthologs. There are only 14 non-conservative substitutions in the two myosin heavy chains, three of which are located in the secondary actin-binding loop and flanking regions and others correspond to residues so far not assigned a functional role, including two residues in the proximal S2 domain. Interestingly, in some of these positions the rat beta/slow myosin heavy chain has the same residues found in human cardiac alpha myosin, a fast-type myosin, and fast skeletal myosins. These observations indicate that functional and structural analysis of myosin orthologs with limited sequence diversity can provide useful clues to identify amino acid residues involved in modulating myosin function.
为了确定导致直系同源肌节肌球蛋白功能多样性的结构差异，我们比较了大鼠和人类的β/慢肌球蛋白。功能比较表明，在体外运动测定中，大鼠β/慢肌球蛋白具有更高的ATP酶活性，并且能以更高的速度移动肌动蛋白丝，相比之下人类β/慢肌球蛋白则不然。序列分析表明，在25 kDa和50 kDa结构域交界处的环区（环1）以及50 kDa和20 kDa结构域交界处的环区（环2），这两个区域被认为与肌球蛋白重链的功能多样性有关，在这两种直系同源物中基本相同。在这两种肌球蛋白重链中只有14个非保守性替换，其中三个位于二级肌动蛋白结合环及其侧翼区域，其他替换对应的残基目前尚未确定其功能作用，包括近端S2结构域中的两个残基。有趣的是，在其中一些位置，大鼠β/慢肌球蛋白重链具有与人类心脏α肌球蛋白（一种快型肌球蛋白）以及快肌骨骼肌肌球蛋白中相同的残基。这些观察结果表明，对序列多样性有限的肌球蛋白直系同源物进行功能和结构分析，可以为识别参与调节肌球蛋白功能的氨基酸残基提供有用的线索。
