Calcium regulates striated muscle contraction through structural changes where the troponin arm binds actin at low calcium levels, causing tropomyosin to block myosin-binding sites.
This review elucidates the structural mechanism by which calcium regulates striated muscle contraction via conformational changes in the troponin-tropomyosin complex.
The author reviewed the research that led to establish the structural basis for the mechanism of the calcium-regulation of the contraction of striated muscles. The target of calcium ions is troponin on the thin filaments, of which the main component is the double-stranded helix of actin. A model of thin filament was generated by adding tropomyosin and troponin. During the process to provide the structural evidence for the model, the troponin arm was found to protrude from the calcium-depleted troponin and binds to the carboxyl-terminal region of actin. As a result, the carboxyl-terminal region of tropomyosin shifts and covers the myosin-binding sites of actin to block the binding of myosin. At higher calcium concentrations, the troponin arm changes its partner from actin to the main body of calcium-loaded troponin. Then, tropomyosin shifts back to the position near the grooves of actin double helix, and the myosin-binding sites of actin becomes available to myosin resulting in force generation through actin-myosin interactions.
Takeyuki Wakabayashi (Thu,) conducted a review in Striated muscle contraction. Calcium regulates striated muscle contraction through structural changes where the troponin arm binds actin at low calcium levels, causing tropomyosin to block myosin-binding sites.
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