Cardiac ventricular myosin and slow skeletal myosin exhibit dissimilar chemomechanical properties despite bearing the same myosin heavy chain isoform

The myosin II motors are ATP-powered force-generating machines driving cardiac and muscle contraction. Myosin II heavy chain isoform-beta (β-MyHC) is primarily expressed in the ventricular myocardium and in slow-twitch muscle fibers, such as M. soleus. M. soleus–derived myosin II (SolM-II) is often used as an alternative to the ventricular β-cardiac myosin (βM-II); however, the direct assessment of biochemical and mechanical features of the native myosins is limited. By employing optical trapping, we examined the mechanochemical properties of native myosins isolated from the rabbit heart ventricle and soleus muscles at the single-molecule level. We found purified motors from the two tissue sources, despite expressing the same MyHC isoform, displayed distinct motile and ATPase kinetic properties. We demonstrate βM-II was approximately threefold faster in the actin filament–gliding assay than SolM-II. The maximum actomyosin (AM) detachment rate derived in single-molecule assays was also approximately threefold higher in βM-II, while the power stroke size and stiffness of the “AM rigor” crossbridge for both myosins were comparable. Our analysis revealed a higher AM detachment rate for βM-II, corresponding to the enhanced ADP release rates from the crossbridge, likely responsible for the observed differences in the motility driven by these myosins. Finally, we observed a distinct myosin light chain 1 isoform (MLC1sa) that associates with SolM-II, which might contribute to the observed kinetics differences between βM-II and SolM-II. These results have important implications for the choice of tissue sources and justify prerequisites for the correct myosin heavy and light chains to study cardiomyopathies. The myosin II motors are ATP-powered force-generating machines driving cardiac and muscle contraction. Myosin II heavy chain isoform-beta (β-MyHC) is primarily expressed in the ventricular myocardium and in slow-twitch muscle fibers, such as M. soleus. M. soleus–derived myosin II (SolM-II) is often used as an alternative to the ventricular β-cardiac myosin (βM-II); however, the direct assessment of biochemical and mechanical features of the native myosins is limited. By employing optical trapping, we examined the mechanochemical properties of native myosins isolated from the rabbit heart ventricle and soleus muscles at the single-molecule level. We found purified motors from the two tissue sources, despite expressing the same MyHC isoform, displayed distinct motile and ATPase kinetic properties. We demonstrate βM-II was approximately threefold faster in the actin filament–gliding assay than SolM-II. The maximum actomyosin (AM) detachment rate derived in single-molecule assays was also approximately threefold higher in βM-II, while the power stroke size and stiffness of the “AM rigor” crossbridge for both myosins were comparable. Our analysis revealed a higher AM detachment rate for βM-II, corresponding to the enhanced ADP release rates from the crossbridge, likely responsible for the observed differences in the motility driven by these myosins. Finally, we observed a distinct myosin light chain 1 isoform (MLC1sa) that associates with SolM-II, which might contribute to the observed kinetics differences between βM-II and SolM-II. These results have important implications for the choice of tissue sources and justify prerequisites for the correct myosin heavy and light chains to study cardiomyopathies. 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The for from a that the is for the between the two is an 1 (MLC1sa) that is expressed in muscle found in the Our the of the The light chains and contribute to the kinetic and differences is for at the molecular isoform and cardiomyopathies. Our was to the of β-cardiac and myosin features as the same that native β-cardiac and myosin are to as βM-II and SolM-II, β-cardiac myosin motors were from the rabbit heart ventricle and examined in the for The heavy chain and light chain of the purified motors were examined for myosins The light chains corresponding to heavy chain were observed in the of and were in a of The distinct to and corresponding and were than which is in βM-II myosin II were from the rabbit found in slow-twitch muscles The isolated were for to myosin II isoform expressed in in M. as in the ventricular myosin was with the myosin for heavy and light chain and The of two and was for the myosin (SolM-II) and for the ventricular myosin The isolated motors were actin assay in We of the driven by βM-II and SolM-II. to the in the of were in the same in the actin was to the for both βM-II and SolM-II. 1 a of actin as a of from to The with an in and the the were threefold higher for βM-II than at By the to the of and were for βM-II and SolM-II, The was also that and for the βM-II and SolM-II, are by the rate of AM crossbridge of the between and cardiac ADP release rates from myosin heavy chain the of muscle The are the that the the of the AM and the power stroke size of that the AM crossbridge the of the ATPase myosin to actin is as the The by a in the rate from the AM the rate of of AM to that is the of the myosin motors in the The myosin a of and muscle myosin both at in Myosin from of actin of heavy myosin were the the observed differences in the for βM-II and likely from power stroke size the of the both at the of the observed differences in the we single-molecule analysis and the biochemical and mechanical properties of The optical assay in is to optical to the and mechanical to the study of actin is between the two myosin motors are the in is and The the between myosin and actin as a in the of The mechanical of myosin with actin is with the from to with the of a power stroke the actin is by the myosin for an AM the of the primarily the the power that the to the release is that of the and biochemical in the myosin power M. the in by cardiac is to have to the of the observed We that the the stroke and The of the the and the is to the of in the the to the of the ADP release rate and AM detachment rate is to rate of ADP The (AM) were at to study the of the We used the of from 1 to and the of at for is an as for in The of is used to the rate in the of the detachment rate the maximum detachment rate of and the that the to detachment rate of that the were as the were for the detachment rates of cardiac myosin βM-II were with the myosin and displayed threefold maximum detachment rate than was also for SolM-II, that βM-II the AM detachment kinetic properties between the and SolM-II. 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