Key result
The presence of a non-motile G680V mutant myosin motor increased the sliding velocity of actin filaments on skeletal muscle myosin molecules by about two-fold compared to skeletal HMM alone.
The presence of a non-motile mutant myosin motor paradoxically accelerates the sliding velocity of actin filaments driven by skeletal muscle myosin in vitro.
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Hypothesis-generating for myosin mutation mechanics in muscle dysfunction; leaves open how these altered.
We examined the movement of an actin filament sliding on a mixture of normal and genetically modified myosin molecules that were attached to a glass surface. For this purpose, we used a Dictyostelium G680V mutant myosin II whose release rates of Pi and ADP were highly suppressed relative to normal myosin, leading to a significantly extended life-time of the strongly bound state with actin and virtually no motility. When the mixing ratio of G680V mutant myosin II to skeletal muscle HMM (heavy myosin) was 0.01%, the actin filaments moved intermittently. When they moved, their sliding velocities were about two-fold faster than the velocity of skeletal HMM alone. Furthermore, sliding movements were also faster when the actin filaments were allowed to slide on skeletal muscle HMM-coated glass surfaces in the motility buffer solution containing G680V HMM. In this case no intermittent movement was observed. When the actin filaments used were copolymerized with a fusion protein consisting of Dictyostelium actin and Dictyostelium G680V myosin II motor domain, similar faster sliding movements were observed on skeletal muscle HMM-coated surfaces. The filament sliding velocities were about two-fold greater than the velocities of normal actin filaments. We found that the velocity of actin filaments sliding on skeletal muscle myosin molecules increased in the presence of a non-motile G680V mutant myosin motor.
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Iwase et al. (2017) studied this question. Dictyostelium G680V mutant myosin II vs. skeletal muscle HMM alone was evaluated on sliding velocity of actin filaments. The presence of a non-motile G680V mutant myosin motor increased the sliding velocity of actin filaments on skeletal muscle myosin molecules by about two-fold compared to skeletal HMM alone.
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