The molecular effects of skeletal muscle myosin regulatory light chain phosphorylation.
Phosphorylation of the myosin regulatory light chain (RLC) in skeletal muscle has been proposed to act as a molecular memory of recent activation by increasing the rate of force development, ATPase activity, and isometric force at submaximal activation in fibers. It has been proposed that these effects stem from phosphorylation-induced movement of myosin heads away from the thick filament backbone. In this study, we examined the molecular effects of skeletal muscle myosin RLC phosphorylation using in vitro motility assays. We showed that, independently of the thick filament backbone, the velocity of skeletal muscle myosin is decreased upon phosphorylation due to an increase in the myosin duty cycle. Furthermore, we did not observe a phosphorylation-dependent shift in calcium sensitivity in the absence of the myosin thick filament. These data suggest that phosphorylation-induced movement of myosin heads away from the thick filament backbone explains only part of the observed phosphorylation-induced changes in myosin mechanics. Last, we showed that the duty cycle of skeletal muscle myosin is strain dependent, consistent with the notion that strain slows the rate of ADP release in striated muscle.
Greenberg
Michael J
MJ
Dept. of Physiology and Biophysics, Boston Univ. School of Medicine, 72 E. Concord St., Boston, MA 02118, USA.
Mealy
Tanya R
TR
Watt
James D
JD
Jones
Michelle
M
Szczesna-Cordary
Danuta
D
Moore
Jeffrey R
JR
D000185:Actinin / Q000737:chemistry; D000199:Actins / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000465:Algorithms; D000469:Alkaline Phosphatase / Q000737:chemistry; D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000737:chemistry; D002147:Calmodulin / Q000737:chemistry; D009038:Motion; D018994:Myosin Light Chains / Q000737:chemistry* / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000737:chemistry; D010766:Phosphorylation / Q000502:physiology; D011817:Rabbits; D024744:Skeletal Muscle Myosins / Q000737:chemistry* / Q000378:metabolism*; D013696:Temperature; D014335:Tropomyosin / Q000737:chemistry; D014336:Troponin / Q000737:chemistry
D000199:Actins; D002147:Calmodulin; D018994:Myosin Light Chains; D014335:Tropomyosin; D014336:Troponin; D000185:Actinin; D000255:Adenosine Triphosphate; D009219:Myosin-Light-Chain Kinase; D000469:Alkaline Phosphatase; D024744:Skeletal Muscle Myosins; D002118:Calcium