Craig R, Smith R, Kendrick-Jones J
Nature. 1983;302(5907):436-9. doi: 10.1038/302436a0.
Phosphorylation of the 20,000-molecular weight (Mr) light chains of vertebrate non-muscle (thymus) and smooth muscle (gizzard) myosins regulates the assembly of these myosins into filaments in vitro. At physiological ionic strength and pH, nonphosphorylated smooth muscle and non-muscle myosin filaments are disassembled by stoichiometric levels of MgATP, forming species having sedimentation coefficients of approximately 11S (range 10-12S; myosin monomers in high salt sediment at 6S). When the 20,000 (20K)-Mr light chains on these 11S myosin species are phosphorylated by the light-chain kinase/calmodulin-Ca2+ complex, the inhibitory effect of the light chains on filament formation is removed and the myosins reassemble into filaments which are stable in MgATP. It was originally suggested that the 11S myosin species was a dimer, previously suggested as a building block for smooth muscle and non-muscle myosin filaments. It has since been shown, however, that 11S smooth muscle myosin is monomeric and has a folded conformation rather than the extended shape characteristic of monomeric myosin in high salt. Here we show that 11S non-muscle myosin is also folded and that phosphorylation of the 20K-Mr light chains of both vertebrate non-muscle (thymus) and vertebrate smooth muscle (gizzard) myosins causes these folded 11S molecules to unfold into the conventional extended monomeric form, which is able to assemble into filaments.
脊椎动物非肌肉（胸腺）和平滑肌（砂囊）肌球蛋白20,000分子量（Mr）轻链的磷酸化在体外调节这些肌球蛋白组装成丝。在生理离子强度和pH值下，非磷酸化的平滑肌和非肌肉肌球蛋白丝被化学计量水平的MgATP拆解，形成沉降系数约为11S的物种（范围10 - 12S；高盐条件下肌球蛋白单体沉降系数为6S）。当这些11S肌球蛋白物种上的20,000（20K）-Mr轻链被轻链激酶/钙调蛋白 - Ca2 +复合物磷酸化时，轻链对丝形成的抑制作用被消除，肌球蛋白重新组装成在MgATP中稳定的丝。最初有人提出11S肌球蛋白物种是一种二聚体，之前被认为是平滑肌和非肌肉肌球蛋白丝的构建块。然而，后来已表明，11S平滑肌肌球蛋白是单体的，具有折叠构象，而不是高盐条件下单体肌球蛋白特有的伸展形状。在这里我们表明，11S非肌肉肌球蛋白也是折叠的，并且脊椎动物非肌肉（胸腺）和平滑肌（砂囊）肌球蛋白的20K-Mr轻链的磷酸化导致这些折叠的11S分子展开成常规的伸展单体形式，从而能够组装成丝。
