The study demonstrates that ADP binding induces asymmetry between the heads of unphosphorylated myosin, providing insights into how motor protein heads may gate each other's responses.
No immediate clinical implications for cardiology; leaves open whether myosin head asymmetry modulates human cardiac contractility.
Light chain phosphorylation is the key event that regulates smooth and non-muscle myosin II ATPase activity. Here we show that both heads of smooth muscle heavy meromyosin (HMM) bind tightly to actin in the absence of nucleotide, irrespective of the state of light chain phosphorylation. In striking contrast, only one of the two heads of unphosphorylated HMM binds to actin in the presence of ADP, and the heads have different affinities for ADP. This asymmetry suggests that phosphorylation alters the mechanical coupling between the heads of HMM. A model that incorporates strain between the two heads is proposed to explain the data, which have implications for how one head of a motor protein can gate the response of the other.
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Berger et al. (2001) studied this question.
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