Two functional heads are required for full activation of smooth muscle myosin.
The motor activity of smooth muscle myosin II is regulated by the regulatory light chain phosphorylation, but it is not understood how phosphorylation activates motor activity. To address this question, we produced asymmetric heavy meromyosin (HMM), which is composed of a wild-type (WT) heavy chain and a mutant heavy chain having no motor activity (i.e. S236T or G457A). The actin-activated ATPase activities (Vmax) of asymmetric HMMs were only 21.8 and 8.4% of the wild-type HMM for S236A/WT HMM and G456A/WT HMM, respectively. If the two heads of HMM are independent for their ATPase activities, asymmetric HMM should show 50% of the activity of wild-type HMM; however, the activity of asymmetric HMM was much lower than the expected value. The results suggest that the activity of the wild-type head is attenuated by the presence of inactive head. Consistently, the actin-gliding velocity of the asymmetric HMM (i.e. S236T/WT or G457A/WT) was less than one-fifth of the wild-type HMM. The present study supports an idea that the two heads of smooth muscle myosin II interact with each other and the presence of two active heads is required for full activation.
Li
Xiang-dong
XD
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Ikebe
Mitsuo
M
D000199:Actins / Q000737:chemistry / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D016367:Baculoviridae / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D027682:Cation Transport Proteins; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D005822:Genetic Vectors; D006868:Hydrolysis; D007313:Insecta; D007700:Kinetics; D018482:Muscle, Skeletal / Q000378:metabolism; D009130:Muscle, Smooth / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D009154:Mutation; D015879:Myosin Subfragments / Q000737:chemistry; D009218:Myosins / Q000737:chemistry / Q000502:physiology*; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014422:Turkeys; D014981:Xenopus
D000199:Actins; D027682:Cation Transport Proteins; D015879:Myosin Subfragments; D011994:Recombinant Proteins; D000251:Adenosine Triphosphatases; C022761:potassium transporting ATPase; D009218:Myosins; D000252:Calcium-Transporting ATPases