Study of Dynamic Properties of Actin Monomer by Normal Mode Analysis.

Abstract

Normal mode analysis of G-actin elucidates the dynamic properties at the molecular level, which should concern the actomyosin contraction motion. In 1990, Holmes published 3-D molecular structure data, determined by X-ray crystalline structure analysis. The minimum energy conformations of G-actin in four cases, with ATP or without ATP, and proK-actin-cut off between Met-47 and Gly-48-or normal actin, were determined by the steepest-descent method and the conjugate-gradient method in the molecular mechanics calculation. The fluctuations of these four actins are studied by the normal mode analysis which is based on the quadratic approximation of the conformational energy function. Root-mean-square atomic fluctuations (r. m. s. fluctuations) reveal the deformability of the conformation at the atomic level. The values of r. m. s. atomic fluctuations of proK-actin are less than those of normal G-actin. This means less functional ability for the actomyosin sliding motion because of less deformability of the 3-D molecular structure. This tendency is suppressed in both cases without ATP. In particular, the existence of ATP exaggerates the fluctuation in the case of G-actin. We also confirm that G-actin with ATP is softer having a higher value of specific volume, than the cases without ATP and with cut-off peptide bonding. We conclude that the softer the actin-e. g., G-actin with ATP-the greater the functional ability for actomyosin sliding motion.