TWO CLASSES OF MYOSIN INHIBITORS, BLEBBISTATIN AND MAVACAMTEN, STABILIZE Β-Cardiac MYOSIN IN DIFFERENT STRUCTURAL AND FUNCTIONAL STATES

Abstract

In addition to a conventional relaxed state, a fraction of myosins in the cardiac muscle exists in a newly-discovered low-energy consuming super-relaxed (SRX) state, which is kept as a reserve pool that may be engaged under sustained increased cardiac demand. The conventional and the super-relaxed states are widely assumed to correspond respectively to a structure where myosin heads are in an open configuration, free to interact with actin, and a closed configuration, inhibiting binding to actin. Disruption of the SRX population in different heart diseases, such as hypertrophic cardiomyopathy, results in unwarranted muscle contraction, and stabilizing them using myosin inhibitors is budding as an attractive therapeutic strategy. Here we examine the structure-function relationships of two myosin ATPase inhibitors, mavacamten, and blebbistatin, and found that binding of mavacamten to myosin at a site different than blebbistatin populates myosin into the SRX state. Blebbistatin, and para-nitroblebbistatin, binding to a distal pocket to the myosin lever arm near the nucleotide-binding site, does not affect the usual myosin SRX state but instead appears to render myosin into a new, perhaps non-functional, ‘ultra-relaxed’ state. X-ray scattering-based rigid body modeling shows that both mavacamten and para-nitroblebbistatin induce novel conformations that diverge significantly from the hypothetical open and closed states and furthermore, mavacamten treatment causes a greater compaction than para-nitroblebbistatin. Taken together, we conclude that mavacamten and blebbistatin stabilize myosin in different structural states, and such states may give rise to different functional energy-sparing SRX states.

Structural basis of the super- and hyper-relaxed states of myosin II

“…1 B), but the fraction of SRX now reaches 60-75% (Stewart et al, 2010;Cooke, 2011). A similar, greatly increased fraction of SRX heads is found in slow skeletal and cardiac muscle fibers and myofibrils (Stewart et al, 2010;Hooijman et al, 2011;McNamara et al, 2017;Nelson et al, 2020;Gollapudi et al, 2021a). In filaments, IHMs undergo intermolecular Molecules in filaments have SRX and DRX turnover rates similar to those of isolated molecules (25-heptad IHM; cf.…”

“…These observations are consistent with the conclusion that in tarantula, intermolecular interaction with S2 from the neighboring crown is responsible for the HRX state. Note that the "ultra-relaxed" state induced in myosin by the inhibitor blebbistatin (Gollapudi et al, 2021a) has a very different origin from the HRX-the former due to internal stabilization of switch 2 in the myosin head in the closed state, inhibiting phosphate release (Zhao et al, 2008), the latter to the external structural constraints on head movements that we have described here. Hu et al, 2016) show interactions between IHMs along the helical tracks (arrows), involving the FH motor domain at one level and the BH lever arm at the next.…”

Divergent Molecular Phenotypes in Point Mutations at the Same Residue in Beta-Myosin Heavy Chain Lead to Distinct Cardiomyopathies

“…The trending increase in the DRX state in HCM-I467V S1 suggests that this mutation may also increase the number of heads that are biochemically available to interact with actin (Figure 2A and 2B). Importantly, a small molecule therapy selective for cardiac myosin heavy chain, Camzyos ® (formerly mavacamten) has been shown to reduce the number of myosin heads that are available to bind to actin [24,[38][39][40]. Thus, based on the data herein, Camzyos may be potential therapy for treatment of HCM caused by β-MHC I467V.…”