title: Role of residues 230 and 236 of actin in myosin-ATPase activation by actin-tropomyosin.
abstract: 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.
authors.affiliation: Department of Physics, School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Saeki
authors.forename: T
authors.initials: T
authors.lastname: Yasunaga
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuura
authors.forename: T
authors.initials: T
authors.lastname: Wakabayashi
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D004023:Dictyostelium / Q000378:metabolism; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009218:Myosins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D014335:Tropomyosin / Q000378:metabolism
chemical_list: D000199:Actins; D014335:Tropomyosin; D009218:Myosins