Recombinant N-terminal domains of MyBP-C reduced actin filament velocity under maximal activation but increased speed under submaximal activation, suggesting they slow cross-bridge cycling kinetics.
The N-terminal domains of MyBP-C slow cross-bridge cycling kinetics by reducing rates of cross-bridge detachment, providing mechanistic insight into its role in regulating myocyte power output.
Myosin binding protein-C (MyBP-C) is a thick-filament protein whose precise function within the sarcomere is not known. However, recent evidence from cMyBP-C knock-out mice that lack MyBP-C in the heart suggest that cMyBP-C normally slows cross-bridge cycling rates and reduces myocyte power output. To investigate possible mechanisms by which cMyBP-C limits cross-bridge cycling kinetics we assessed effects of recombinant N-terminal domains of MyBP-C on the ability of heavy meromyosin (HMM) to support movement of actin filaments using in vitro motility assays. Here we show that N-terminal domains of cMyBP-C containing the MyBP-C "motif," a sequence of approximately 110 amino acids, which is conserved across all MyBP-C isoforms, reduced actin filament velocity under conditions where filaments are maximally activated (i.e. either in the absence of thin filament regulatory proteins or in the presence of troponin and tropomyosin and high Ca2+). By contrast, under conditions where thin filament sliding speed is submaximal (i.e. in the presence of troponin and tropomyosin and low Ca2+), proteins containing the motif increased filament speed. Recombinant N-terminal proteins also bound to F-actin and inhibited acto-HMM ATPase rates in solution. The results suggest that N-terminal domains of MyBP-C slow cross-bridge cycling kinetics by reducing rates of cross-bridge detachment.
Razumova et al. (2006) studied this question. Recombinant N-terminal domains of MyBP-C was evaluated on Actin filament velocity and acto-HMM ATPase rates. Recombinant N-terminal domains of MyBP-C reduced actin filament velocity under maximal activation but increased speed under submaximal activation, suggesting they slow cross-bridge cycling kinetics.