Key result
The G146V mutation in actin altered its structural dynamics and conformation in the presence of skeletal muscle heavy meromyosin, leading to motility defects in myosin II but not myosin V.
The G146V mutation alters actin conformation in a myosin class-specific manner, explaining its selective motility defects with skeletal myosin II but not myosin V.
G146V actin effects remain preclinical; leaves open translation to human cardiac or skeletal muscle disorders.
The structural dynamics of actin, including the tilting motion between the small and large domains, are essential for proper interactions with actin-binding proteins. Gly146 is situated at the hinge between the two domains, and we previously showed that a G146V mutation leads to severe motility defects in skeletal myosin but has no effect on motility of myosin V. The present study tested the hypothesis that G146V mutation impaired rotation between the two domains, leading to such functional defects. First, our study showed that depolymerization of G146V filaments was slower than that of wild-type filaments. This result is consistent with the distinction of structural states of G146V filaments from those of the wild type, considering the recent report that stabilization of actin filaments involves rotation of the two domains. Next, we measured intramolecular FRET efficiencies between two fluorophores in the two domains with or without skeletal muscle heavy meromyosin or the heavy meromyosin equivalent of myosin V in the presence of ATP. Single-molecule FRET measurements showed that the conformations of actin subunits of control and G146V actin filaments were different in the presence of skeletal muscle heavy meromyosin. This altered conformation of G146V subunits may lead to motility defects in myosin II. In contrast, distributions of FRET efficiencies of control and G146V subunits were similar in the presence of myosin V, consistent with the lack of motility defects in G146V actin with myosin V. The distribution of FRET efficiencies in the presence of myosin V was different from that in the presence of skeletal muscle heavy meromyosin, implying that the roles of actin conformation in myosin motility depend on the type of myosin.
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Noguchi et al. (2015) studied this question. G146V mutant actin vs. Wild-type actin was evaluated on Depolymerization rate and FRET efficiency distributions. The G146V mutation in actin altered its structural dynamics and conformation in the presence of skeletal muscle heavy meromyosin, leading to motility defects in myosin II but not myosin V.
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