The influence of myosin phosphorylation on mechanical and metabolical properties of fast twitch skeletal muscle

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The primary structural and enzymatic protein of skeletal muscle is the myosin molecule. The basis of skeletal muscle contraction, and thus movement, is the conversion of chemical energy to mechanical energy by the myosin motor molecule. A key structural element of the myosin molecule is the "regulatory light chain" (R-LC). During muscle activity, the R-LC is chemically modified by the addition of a phosphate ion, an enzymatically regulated process known as "myosin R-LC phosphorylation". Biochemical studies indicate that myosin R-LC phosphorylation may alter myosin motor properties to enhance muscle force, a phenomenon called "force potentiation". The aim of my long term research program is to understand how, why and when myosin R-LC phosphorylation-mediated force potentiation modifies mechanical and metabolic aspects of how fatigued and/or unfatigued skeletal muscle functions. To this end we will perform a variety of experiments examining mechanical and metabolic properties of mouse muscle, a common scientific model for this type of work. The special qualities of this work are that we will perform these studies using genetically engineered mice that lack the gene coding for the enzyme that regulates myosin R-LC phosphorylation and which thus do not exhibit myosin R-LC phosphorylation during activity. Use of these "knockout" mice will allow us to study muscle activity in the absence of myosin R-LC phosphorylation, a situation that does not normally occur, and thus allow us to unequivocally determine the influence of this event on muscle function. We believe that an integrative approach examining the interaction of myosin R-LC phosphorylation with muscle mechanics, intracellular calcium homeostasis and muscle energetics, in both knockout and normal mice, will provide key insights into the physiological role and mechanism of action of myosin R-LC phosphorylation for skeletal muscle function. This type of information is vitally important because there is much current interest in how myosin R-LC phosphorylation modulates performance of healthy and diseased human skeletal muscle, and our work will provide important new directions for future work in this area.