Influence of 2,3-Butanedione Monoxime on the Actin–Myosin Interaction in Modeling Healthy Function and Congenital Myopathy in a Single Muscle Fiber

Congenital myopathies are a heterogeneous group of human skeletal muscle disorders characterized by muscle hypotonia and weakness. The clinical picture of myopathies differs significantly in different patients, which makes it extremely difficult to diagnose the myopathy variant and develop treatment approaches. There are several pharmacological agents in clinical use or under clinical investigation for the treatment of cardiomyopathies, the mechanism of action of which can also be used to treat congenital myopathies. One such agent is 2,3-butanedione monoxime (BDM), a noncompetitive inhibitor of myosin ATPase activity used to suppress acute myocardial injury. Molecular mechanisms of myosin inhibition in the presence of BDM in skeletal muscle have not been studied, so the aim of this work was to study the effect of this agent on the interaction of myosin with actin in modeling several stages of the ATPase cycle in skeletal muscle fiber in order to assess the prospects for the use of BDM for the treatment of congenital myopathies. We found that BDM, in the absence of the regulatory proteins tropomyosin and troponin, enhances the rigidity of myosin binding to actin while modeling the weak binding of these muscle proteins, which can slow down the transition of actomyosin from the A∙M∙ADP∙Pi state to the A∙M∙ADP state and is one of the reasons for the decrease in the ATPase activity of myosin. When modeling the successive stages of the ATPase cycle using ADP, AMPPNP, ATPγS, and ATP, the myosin heads gradually switch to a state of weak interaction with actin. In the presence of tropomyosin and troponin in the muscle fiber, BDM does not affect the formation of a weak form of actomyosin binding, but increases the number of myosin heads essential for force generation. BDM can be used to increase the efficiency of myosin conformational rearrangements in the presence of tropomyosin with the R90P mutation associated with congenital myopathy, since this reagent increases the number of myosin heads in the muscle fiber capable of effective conformational rearrangements in the ATPase cycle and partially inhibits the pathological effects of the mutation.