This work, lead by first authors Sarah Clippinger-Schulte and Brent Scott, shows that regulatory proteins in cardiac muscle act via a steric blocking mechanism at physiological ATP concentrations. These proteins do not affect myosin’s mechanics or load dependence.
Interestingly, we see that regulatory proteins tune the kinetics of cardiac myosin’s interactions with the thin filament at low, non-physiological ATP concentrations, suggesting biophysical mechanisms that cannot be explained using conventional models.
The behavior of cardiac myosin interacting with regulated thin filaments is different from other regulated actomyosin systems where these proteins can tune myosin’s mechanics and kinetics, highlighting the diverse roles of regulatory proteins in the cell.
The paper can be found here.