Cooperative Activation of Striated Muscle Thick Filaments by S2 Binding
BIOPHYSICAL JOURNAL(2018)
摘要
Myosin binding protein C (MyBPC) is present at a very low ratio relative to myosin in muscle yet has a significant impact on contractility in cardiomyopathies. One explanation is that MyBPC cooperatively modulates the binding of the S1 to the S2 coiled coil. To test this hypothesis, the MF30 monoclonal antibody is used to compete with MyBPC for binding S2. As a control, the MF20 monoclonal antibody which binds to light meromyosin does not affect muscle contraction. Expansion microscopy of myofibrils reveals that MF30 but not MF20 has reduced labeling in the region of MyBPC binding consistent with competition between MF30 and MyBPC. Designed antiS2 synthetic peptides that modulate myosin S2 stability demonstrate cooperativity similar to MF30 with higher measured Kd values than their EC50 or IC50 on myofibril contractility. Furthermore, fluorescent labeling of the antiS2 peptides reduces their binding affinity but not the extent of their effect on myofibril contractility. The antiS2 peptide that destabilizes the coiled coil had a greater maximum enhancement of myofibril contractility than MF30 which suggests that the peptide may block the binding of S1 to S2 while MF30 may simply act by sterically blocking MyBPC. Furthermore, MF30 has no effect on in vitro motility assays of purified actin and myosin; while the destabilizing peptide slightly enhanced actin sliding velocities. These results support the view that a cooperative transition occurs between less active and more active conformations of myosin in the thick filament that can be modulated by a substoichiometric amount of effector.
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关键词
striated muscle thick filaments,striated muscle,cooperative activation
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