A230Y mutation of actin on subdomain 4 is sufficient for higher calcium activation of actin-activated myosin adenosinetriphosphatase in the presence of tropomyosin-troponin.
To probe the mechanism by which Ca(2+) activates muscle contraction through tropomyosin and troponin, we have produced mutant actins using Dictyostelium discoideum. We focused on the sequence 228-232 (QTAAS) that is located in subdomain 4 of actin, because the chimera actin in which this sequence was replaced by KAYKE showed not only poorer tropomyosin binding but also the unexpected "higher Ca(2+) activation" [Saeki, K., et al. (1996) Biochemistry 35, 14465-14472]. We found that this higher Ca(2+) activation is solely due to the A230Y mutagenesis. Because A230Y mutant actin showed normal tropomyosin binding, the higher Ca(2+) activation is not the consequence of poorer tropomyosin binding. The significance of these results is discussed in view of a three-state model [McKillop, D. F., Geeves, M. A. (1993) Biophys. J. 65, 693-701].
Saeki
K
K
Department of Physics, School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
Wakabayashi
T
T
D000199:Actins / Q000235:genetics* / Q000502:physiology; D000409:Alanine / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004023:Dictyostelium / Q000235:genetics; D004789:Enzyme Activation; D018482:Muscle, Skeletal / Q000201:enzymology; D016297:Mutagenesis, Site-Directed; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation; D011485:Protein Binding / Q000235:genetics; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014335:Tropomyosin / Q000378:metabolism / Q000502:physiology*; D014336:Troponin / Q000502:physiology*; D014443:Tyrosine / Q000235:genetics
D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D014335:Tropomyosin; D014336:Troponin; D014443:Tyrosine; D009218:Myosins; D000409:Alanine; D002118:Calcium