Conformational changes linked to ADP release from human cardiac myosin bound to actin-tropomyosin

Abstract

Following binding to the thin filament, β-cardiac myosin couples ATP-hydrolysis to conformational rearrangements in the myosin motor that drive myofilament sliding and cardiac ventricular contraction. However, key features of the cardiac-specific actin-myosin interaction remain uncertain, including the structural effect of ADP release from myosin, which is rate-limiting during force generation. In fact, ADP release slows under experimental load or in the intact heart due to the afterload, thereby adjusting cardiac muscle power output to meet physiological demands. To further elucidate the structural basis of this fundamental process, we used a combination of cryo-EM reconstruction methodologies to determine structures of the human cardiac actin–myosin–tropomyosin filament complex at better than 3.4 Å-resolution in the presence and in the absence of Mg2+·ADP. Focused refinements of the myosin motor head and its essential light chains in these reconstructions reveal that small changes in the nucleotide-binding site are coupled to significant rigid body movements of the myosin converter domain and a 16-degree lever arm swing. Our structures provide a mechanistic framework to understand the effect of ADP binding and release on human cardiac β-myosin, and offer insights into the force-sensing mechanism displayed by the cardiac myosin motor.

Molecular mechanisms linking missense ACTG2 mutations to visceral myopathy

“…R148 falls near the hydrophobic cleft in actin, which participates in interactions with numerous ABPs and interprotomer contacts in F-actin ( 21 , 22 ). R148 also forms part of the myosin-binding interface ( 23 ). R178 is located near the catalytic site and forms part of the back door through which the γ-phosphate is believed to be released after hydrolysis of the actin-bound nucleotide ( 19 ).…”

“…In contrast, the R40C mutation falls farther away from the binding surfaces of myosin and Tpm (fig. S6) ( 23 ), whose interactions with R40C filaments remained unaffected (Figs. 4E and 5C).…”

“…That myosin and Tpm1.4 do not discriminate between these filaments is not unexpected; α-actin and ACTG2 share 98.4% sequence identity, and the mutations R40C and R257C do not affect the binding surfaces of Tpm nor myosin (fig. S6) ( 23 ). Collectively, our observations suggest that R40C is likely to cause disease through its markedly compromised polymerization.…”

Structural electrochemistry of poly(3,4-ethylenedioxythiophene) and its applicability as simultaneous sensor of environmental surroundings: self-sensing electrical, thermal, and chemical working conditions

“…1 The working of biological muscles is based on the electrical signals generated in the brain; send to the muscle through the motor neuron, liberating Ca 2+ ions in the cell initiating the reaction-driven conformational movements of the actin-myosin-ATP (muscular contraction). 2 Any muscle is an electro-chemo-mechanical organ working by cooperative actuation of the constitutive macromolecular motors (actin-myosin proteins). 3 While actuation biological muscles sense the environment (temperature, pressure, muscle potential and chemical potential in the body), transmitting back this sensing information to the brain through the sensing neuron.…”

Troponin-I–induced tropomyosin pivoting defines thin-filament function in relaxed and active muscle

“…In contrast, the solution of the larger myosin-induced movement of the tropomyosin to the M-state position on actin appears to be less problematic ( Doran et al, 2020 ; Doran et al, 2023a ; Baldo et al, 2021 ). In this case, the reconfiguration is captured as distinct and well-defined M-state end-points ( Milligan et al, 1990 ; Vibert et al, 1997 ; Poole et al, 2006 ; Behrmann et al, 2012 ; Doran et al, 2020 ; Doran et al, 2023a ; Doran et al, 2023b ; Risi et al, 2021b ).…”