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#myosin head

2 public questions tagged with this topic.

Cytoskeleton

In muscle contraction, when does the myosin head detach from actin?

Force production by myosin II follows an ordered ATPase cycle that tightly couples nucleotide state to actin affinity ensuring efficient energy usage. In rigor nucleotide free myosin binds filamentous actin with high affinity angle about 45 degrees maintaining tension. Rapid binding of Mg ATP to nucleotide pocket causes allosteric opening of actin binding cleft dropping affinity thousand fold and triggering swift detachment within milliseconds even before hydrolysis occurs. While detached intrinsic ATPase hydrolyzes ATP to ADP plus inorganic phosphate providing free energy that reorients lever

Ref: Lodish et al., Molecular Cell Biology 9th ed., Chapter 18: Myosin cross-bridge cycle, ATP binding mediated detachment mechanism.

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Cytoskeleton

Myosin head movement along actin filaments is driven by:

Myosin motor cycle couples ATP hydrolysis to filament sliding via conformational changes in conserved motor domain. In absence of ATP myosin head strongly bound to actin in rigor state, stereospecific binding between actin helix and myosin cardiomyopathy loop. Binding of ATP to P loop pocket between upper and lower 50 kilodalton subdomains induces opening of actin binding cleft reducing affinity thousand fold leading to detachment. While detached ATP hydrolyzed to ADP Pi mediated by Switch I Switch II closing around gamma phosphate, triggering recovery stroke where lever arm moves about 90 deg

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 16: Myosin ATP Hydrolysis and Movement.

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