Abstract
Calponin is a thin filament-associated protein in smooth muscle that has been shown to bind actin, tropomyosin and calmodulin, and has been implicated to play a role in regulation of smooth muscle contractility. Using a centrifugation assay we found that calponin interacts with unphosphorylated filamentous smooth muscle myosin. We found that this calponin-myosin interaction is reversed by Ca 2+-CaM, and depends on ionic strength. At 50 mM NaCI the binding constant and the stoichiometry of this interaction were estimated to be 2 × 10 6 M −1, and 1.2–2.4 calponin per myosin, respectively. We suggest that the calponin-myosin interaction could be involved in regulation of smooth muscle contractility by anchoring myosin to actin.
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