Kikumoto Mahito, Tamura Youjiro, Ooi Atsushi, Mihashi Koshin
Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
J Biochem. 2003 May;133(5):687-91. doi: 10.1093/jb/mvg088.
We determined the partial specific volume and partial specific adiabatic compressibility of either ATP- or ADP-bound monomeric actin in the presence of Ca(2+) by measuring the density of and sound velocity in a monomeric actin solution at 18 degrees C. The partial specific volume of ATP-bound monomeric actin, equal to 0.744 cm(3)/g, which is exceptionally high among globular proteins, was reduced to 0.727 cm(3)/g when the tightly bound ATP was replaced with ADP. Associated with this, the adiabatic compressibility of ATP-bound monomeric actin, equal to 8.8 x 10(-12) cm(2)/dyne, decreased to 5.8 x 10(-12) cm(2)/dyne, which is a common value for globular proteins. These results suggested that an extraordinarily soft global conformation of ATP-bound monomeric actin is packed into a compact mass associated with the hydrolysis of bound ATP. When monomeric actin was limitedly proteolyzed at subdomain 2 with subtilisin, the nucleotide-dependent flexibility of the global conformation of monomeric actin was lost.
我们通过测量18摄氏度下单体肌动蛋白溶液的密度和声速，测定了在Ca(2+)存在下与ATP或ADP结合的单体肌动蛋白的偏比容和偏比绝热压缩率。与ATP结合的单体肌动蛋白的偏比容为0.744 cm(3)/g，在球状蛋白中异常高，当紧密结合的ATP被ADP取代时，降至0.727 cm(3)/g。与此相关的是，与ATP结合的单体肌动蛋白的绝热压缩率为8.8×10(-12) cm(2)/达因，降至5.8×10(-12) cm(2)/达因，这是球状蛋白的常见值。这些结果表明，与ATP结合的单体肌动蛋白异常柔软的整体构象在结合的ATP水解时被包装成紧密的聚集体。当单体肌动蛋白在亚结构域2用枯草杆菌蛋白酶进行有限蛋白酶解时，单体肌动蛋白整体构象的核苷酸依赖性灵活性丧失。
