Myosin cleft closure determines the energetics of the actomyosin interaction

Abstract

Formation of the strong binding interaction between actin and myosin is essential for force generation in muscle and in cytoskeletal motor systems. To clarify the role of the closure of myosin's actin-binding cleft in the actomyosin interaction, we performed rapid kinetic, spectroscopic, and calorimetric experiments and atomic-level energetic calculations on a variety of myosin isoforms for which atomic structures are available. Surprisingly, we found that the endothermic actin-binding profile of vertebrate skeletal muscle myosin subfragment-1 is unique among studied myosins. We show that the diverse propensity of myosins for cleft closure determines different energetic profiles as well as structural and kinetic pathways of actin binding. Depending on the type of myosin, strong actin binding may occur via induced-fit or conformational preselection mechanisms. However, cleft closure does not directly determine the kinetics and affinity of actin binding. We also show that cleft closure is enthalpically unfavorable, reflecting the development of an internal strain within myosin in order to adopt precise steric complementarity to the actin filament. We propose that cleft closure leads to an increase in the torsional strain of myosin's central β-sheet that has been proposed to serve as an allosteric energy-transducing spring during force generation.

Molecular mechanisms underlying deoxy‐ADP.Pi activation of pre‐powerstroke myosin

“…The extent to which the actin binding cleft is open vs. closed is thought to predict whether myosin binding to actin is energetically favorable. Open‐cleft conformations of myosin bind to actin endergonic in contrast to closed‐cleft conformations of myosin, which can bind exergonic . We assessed the openness of the actin binding cleft by measuring the angle between the helices bordering the cleft on the lower 50k domain (w‐helix, residues 630–646) and the upper 50k domain (HO helix, residues 411–442).…”

Understanding the Cooperative Interaction between Myosin II and Actin Cross-Linkers Mediated by Actin Filaments during Mechanosensation

“…Biophysical Journal 102(2) 238-247 can be easily adapted for the myosin assembly of other species because the k 1 and k À1 that dictate the reactions have reported values in different systems (30), and the concentrations of F-actin and myosin in the cortex are relatively straightforward to measure.…”

“…Therefore, k À needs to be set numerically. The value k 1 , the rate that controls the conversion from the bound and the unbound states, has the form of k 1 ¼ k on C actin , where k on is the onrate for myosin binding to actin and is~0.45 mM À1 s À1 (30). Because myosin unbinding to actin is force-dependent (8) and the isometric binding state is crucial for cooperativity (22), it is reasonable to incorporate its associated cooperative effect in the rate k À1 that controls the conversion from the bound and the unbound states.…”

Age and sex differences in the ventilatory response to hypoxia and hypercapnia in awake neonatal, pre-pubertal and young adult rats

“…In adult mammals the postulated rhythm generator is comprised of a GABA A -dependent reciprocal inhibition between two medullary nuclei (Fregosi, et al ., 2004; Mellen et al ., 2003; Rybak et al ., 2007). GABA A receptor subunit composition in the rostral ventral respiratory group (rVRG) in rats has been shown to change during pregnancy, when sex hormones are at a physiological peak (Stang et al ., 2011). If GABA A receptor expression was altered on bulbospinal respiratory neurons, changes in ventilation might result (Zuperku and McCrimmon, 2002).…”