Stability of Myosin Subfragment-2 Modulates the Force Produced by Acto-Myosin Interaction of Striated Muscle
Authors:   , Singh Rohit Rajendraprasad 
Published: February 2025

Myosin subfragment-2 (S2) is a coiled coil linker between myosin subfragment-1 and light meromyosin (LMM). This dissertation examines whether the myosin S2 coiled coil could regulate the amount of myosin S1 heads available to bind actin thin filaments by modulating the stability of its coiled coil. A stable myosin S2 coiled coil would have less active myosin S1 heads compared to a more flexible myosin S2 coiled coil, thus causing increased force production through acto-myosin interaction. The stability of the myosin S2 coiled coil was modulated by the binding of a natural myosin S2 binding protein, myosin binding protein C (MyBPC), and synthetic myosin S2 binding proteins, stabilizer and destabilizer peptide, to myosin S2. Competitive enzyme linked immunosorbent assay (cELISA) experiments revealed the cross specificity and high binding affinity of the synthetic peptides to the myosin S2 of human cardiac and rabbit skeletal origins. Gravitational force spectroscopy (GFS) was performed to test the stability of myosin S2 coiled coil in the presence of these myosin S2 binding proteins. GFS experiments demonstrated the stabilization of the myosin S2 coiled coil by the binding of MyBPC and stabilizer peptide to myosin S2, while the binding of destabilizer peptide to the same resulted in a flexible myosin S2 coiled coil. The binding of MyBPC and stabilizer peptide respectively, resulted in 3.35 and 1.5 times increase in force required to uncoil the myosin S2, while the binding of destabilizer peptide resulted in 1.6 times decrease in force required to uncoil the myosin S2. The myofibrillar contractility assay was performed to test the effect of synthetic myosin S2 binding proteins on the sarcomere shortening in myofibrils. The stabilizer peptide resulted in decreased sarcomere shortening of myofibrils as a result of decreased acto-myosin interaction, on the other hand, the binding of destabilizer peptide caused an increase in sarcomere shortening. The in vitro motility assay was performed to test the effect of altered stability of myosin S2 by binding of these myosin S2 binding proteins on the motility of actin filaments sliding over myosin. The motility of actin filaments was hindered by treating myosin thick filaments with whole length skeletal MyBPC or by treating heavy meromyosin with stabilizer peptide, while the motility of actin filaments was enhanced when heavy meromyosin was treated with destabilizer peptide. This study demonstrates that the myosin S2 coiled coil stability influences the force produced by acto-myosin interaction in striated skeletal muscle. The myosin S2 coiled coil when stabilized by MyBPC and stabilizer peptide resulted in decreased force production by reduced acto-myosin interaction. While the binding of destabilizer resulted in a flexible myosin S2 coiled coil and increased force production by enhanced acto-myosin interaction. The potentially cooperative response of contractility to the instability of the S2 coiled coil promises that this biological mechanism may be the target of drugs to modulate muscle performance.