Hemric M E, Lu F W, Shrager R, Carey J, Chalovich J M
Department of Biochemistry, East Carolina University, School of Medicine, Greenville, North Carolina 27858-4354.
J Biol Chem. 1993 Jul 15;268(20):15305-11.
Caldesmon, an actin-binding protein from smooth muscle and non-muscle cells, has previously been shown to bind stoichiometrically to smooth muscle myosin in an ATP-dependent manner. We now show quantitatively the effects of Ca(2+)-calmodulin and phosphorylation on the binding of caldesmon to myosin. Ca(2+)-calmodulin reduces the binding of caldesmon to myosin with the same effectiveness as it does the binding of caldesmon to actin. However, Ca(2+)-calmodulin is ineffective in antagonizing the binding of the purified myosin-binding region of caldesmon to myosin. These and other results suggest that Ca(2+)-calmodulin binding to the COOH-terminal region of caldesmon is responsible for reversal of binding to myosin. Phosphorylation of the NH2-terminal region of caldesmon by the co-purifying kinase, calmodulin-dependent protein kinase II, weakens but does not eliminate the binding of caldesmon to smooth muscle myosin. Finally, phosphorylation of smooth muscle myosin by smooth muscle myosin light chain kinase has no effect on the binding of caldesmon to myosin. Since Ca(2+)-calmodulin and phosphorylation of caldesmon weaken the binding of caldesmon to both actin and myosin, these events may be coordinately regulated.
钙调蛋白是一种来自平滑肌和非肌肉细胞的肌动蛋白结合蛋白，此前已证明它能以ATP依赖的方式与平滑肌肌球蛋白化学计量地结合。我们现在定量地展示了Ca(2+) - 钙调蛋白和磷酸化对钙调蛋白与肌球蛋白结合的影响。Ca(2+) - 钙调蛋白降低钙调蛋白与肌球蛋白结合的效果，与它降低钙调蛋白与肌动蛋白结合的效果相同。然而，Ca(2+) - 钙调蛋白在拮抗钙调蛋白纯化的肌球蛋白结合区域与肌球蛋白的结合方面无效。这些以及其他结果表明，Ca(2+) - 钙调蛋白与钙调蛋白COOH末端区域的结合是导致与肌球蛋白结合逆转的原因。共纯化的激酶钙调蛋白依赖性蛋白激酶II对钙调蛋白NH2末端区域的磷酸化会减弱但不会消除钙调蛋白与平滑肌肌球蛋白的结合。最后，平滑肌肌球蛋白轻链激酶对平滑肌肌球蛋白的磷酸化对钙调蛋白与肌球蛋白的结合没有影响。由于Ca(2+) - 钙调蛋白和钙调蛋白的磷酸化会减弱钙调蛋白与肌动蛋白和肌球蛋白的结合，这些事件可能受到协同调节。
