Key result
In the unphosphorylated state, intramolecular interactions position the actin-binding interface of one head onto the converter domain of the second head, providing a mechanism for inhibition.
This basic science study reveals the structural mechanism of smooth muscle myosin inhibition, demonstrating that intramolecular interactions in the unphosphorylated state block the actin-binding interface.
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Structural differences in myosin inform basic regulation; leaves open translation to vascular therapies.
The structural basis for the phosphoryla- tion-dependent regulation of smooth muscle myosin ATPase activity was investigated by forming two- dimensional (2-D) crystalline arrays of expressed unphosphorylated and thiophosphorylated smooth muscle heavy meromyosin (HMM) on positively charged lipid monolayers. A comparison of averaged 2-D projections of both forms at 2.3-nm resolution reveals distinct structural differences. In the active, thiophosphorylated form, the two heads of HMM interact intermolecularly with adjacent molecules. In the unphosphorylated or inhibited state, intramolecular interactions position the actin-binding interface of one head onto the converter domain of the second head, thus providing a mechanism whereby the activity of both heads could be inhibited.
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Wendt et al. (1999) studied this question. Thiophosphorylation vs. Unphosphorylated state was evaluated on Structural differences in 2-D projections at 2.3-nm resolution. In the unphosphorylated state, intramolecular interactions position the actin-binding interface of one head onto the converter domain of the second head, providing a mechanism for inhibition.
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