Lu F W, Chalovich J M
Department of Biochemistry, East Carolina University, School of Medicine, Greenville, North Carolina 27858-4354, USA.
Biochemistry. 1995 May 16;34(19):6359-65. doi: 10.1021/bi00019a014.
We have reported earlier that ATP causes both an increase in the affinity of caldesmon for smooth muscle myosin and a change in stoichiometry from 2 caldesmon molecules per myosin to 1:1 (Hemric & Chalovich, 1990). We now show that this ATP effect does not occur with skeletal muscle myosin, indicating that ATP has a specific effect on the structure of filamentous smooth muscle myosin. This ATP effect does not appear to be due to stabilization of a 10S type of filamentous smooth muscle myosin like that reported earlier (Ikebe & Hartshorne, 1984) since neither phosphorylation nor extensive modification of myosin with MalNEt (both which stabilize the 6S state of monomeric myosin) eliminates the effect of ATP. Caldesmon does bind more tightly to a form of smooth muscle myosin which is resistant to papain digestion. These results suggest that the ATP effect is due to stabilization of a local conformation of smooth muscle myosin which is independent of the larger 10S/6S conformational change (Suzuki et al., 1988). In the presence of ATP, the two heads of smooth muscle muscle myosin and the S-2 region form a single, higher affinity binding region for caldesmon.
我们之前报道过，ATP会使钙调蛋白与平滑肌肌球蛋白的亲和力增加，并且化学计量比从每分子肌球蛋白结合2个钙调蛋白分子变为1:1（Hemric和Chalovich，1990）。我们现在表明，这种ATP效应在骨骼肌肌球蛋白中不会发生，这表明ATP对丝状平滑肌肌球蛋白的结构有特定作用。这种ATP效应似乎不是由于像之前报道的那样稳定10S型丝状平滑肌肌球蛋白（Ikebe和Hartshorne，1984），因为无论是磷酸化还是用MalNEt对肌球蛋白进行广泛修饰（这两者都能稳定单体肌球蛋白的6S状态）都不能消除ATP的作用。钙调蛋白确实更紧密地结合一种对木瓜蛋白酶消化有抗性的平滑肌肌球蛋白形式。这些结果表明，ATP效应是由于平滑肌肌球蛋白局部构象的稳定，这与更大的10S/6S构象变化无关（Suzuki等人，1988）。在ATP存在的情况下，平滑肌肌球蛋白的两个头部和S-2区域形成了一个对钙调蛋白具有更高亲和力的单一结合区域。
