Saeki K, Yasunaga T, Matsuura Y, Wakabayashi T
Department of Physics, School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
Biochem Biophys Res Commun. 2000 Aug 28;275(2):428-33. doi: 10.1006/bbrc.2000.3321.
The Dictyostelium/Tetrahymena-chimeric actin (Q228K/T229A/A230Y) showed higher Ca(2+)-activation of myosin S1 ATPase in the presence of tropomyosin-troponin. The crystal structure of the chimeric actin is almost the same as that of wild-type except the conformation of the side chain of Leu236. Here, we introduced an additional mutation (L236A), in which the side chain of Leu236 was truncated, into the chimeric actin (Q228K/T229A/A230Y/L236A). Without regulatory proteins, the new mutant actin showed normal myosin S1 activation and normal sliding velocity. However, in the presence of tropomyosin, the new mutant actin activated myosin S1 ATPase higher than the wild-type actin and showed higher velocities in in vitro motility assay at low HMM concentrations. These results suggest that the mutations of A230Y and L236A in the actin subdomain-4 facilitate the transition of thin filaments from a "closed" state to an "open" state.
盘基网柄菌/四膜虫嵌合肌动蛋白（Q228K/T229A/A230Y）在原肌球蛋白 - 肌钙蛋白存在的情况下，对肌球蛋白S1 ATP酶表现出更高的Ca(2+)激活作用。除了Leu236侧链的构象外，嵌合肌动蛋白的晶体结构与野生型几乎相同。在此，我们在嵌合肌动蛋白（Q228K/T229A/A230Y/L236A）中引入了一个额外的突变（L236A），其中Leu236的侧链被截短。在没有调节蛋白的情况下，新的突变型肌动蛋白表现出正常的肌球蛋白S1激活和正常的滑动速度。然而，在原肌球蛋白存在的情况下，新的突变型肌动蛋白比野生型肌动蛋白更能激活肌球蛋白S1 ATP酶，并且在低重链肌球蛋白浓度下的体外运动测定中表现出更高的速度。这些结果表明，肌动蛋白亚结构域4中的A230Y和L236A突变促进了细肌丝从“闭合”状态向“开放”状态的转变。
