The mechanism of Ca2+ regulation of vascular smooth muscle thin filaments by caldesmon and calmodulin.
The mechanism of Ca2+ regulation of vascular smooth muscle thin filaments by caldesmon and calmodulin.
复制标题
钙结合蛋白和钙调蛋白对血管平滑肌细丝的Ca2调节机制。
DOI：
10.1016/s0021-9258(19)75896-7
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Steven B Marston
中科院分区：
文献类型：
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作者：
C. Smith;K. Pritchard;Steven B Marston
在肌动蛋白、原肌球蛋白和钙调蛋白能够形成重组的钙敏感的平滑肌细丝的条件下，测定了血管平滑肌钙调蛋白与肌动蛋白、原肌球蛋白和钙调蛋白的相互作用。Caldesmon以一种复杂的方式与肌动蛋白结合，高亲和力部位(K=10(7)M-1)在化学计量比为每28个肌动蛋白中有1个饱和，而低亲和力部位在每7个肌动蛋白中有1个。在原肌球蛋白存在的情况下，结合的亲和力增加，这可以归因于钙离子与原肌球蛋白之间的直接相互作用，这种作用是用钙离子蒙与琼脂糖交联法证明的。在原肌球蛋白存在的情况下，高亲和力位点的占据与肌动蛋白激活的肌球蛋白镁ATPase活性的抑制有关。在钙离子存在的情况下，Caldesmon与钙调蛋白结合，亲和力为10(6)M-1。钙调素与钙调素的结合与肌动蛋白-原肌球蛋白抑制的中和有关。钙调素结合减少，但不取消钙调素与肌动蛋白原肌球蛋白的结合。根据这一数据，我们提出了一个平滑肌细丝的模型，在该模型中，钙离子通过将被抑制的肌动蛋白-原肌球蛋白-钙调蛋白复合体转化为活性复合体，即肌动蛋白-原肌球蛋白-钙调蛋白X、钙离子和肌动蛋白-原肌球蛋白来调节活性。
The interactions of vascular smooth muscle caldesmon with actin, tropomyosin, and calmodulin were determined under conditions in which the four proteins can form reconstituted Ca2+-sensitive smooth muscle thin filaments. Caldesmon bound to actin in a complex fashion with high affinity sites (K = 10(7) M-1) saturating at a stoichiometry of 1 per 28 actins, and lower affinity sites at 1 per 7 actins. The affinity of binding was increased in the presence of tropomyosin, and this could be attributed to a direct interaction between caldesmon and tropomyosin which was demonstrated using caldesmon cross-linked to Sepharose. In the presence of tropomyosin, occupancy of the high affinity sites was associated with inhibition of actin-activated myosin MgATPase activity. Caldesmon was found to bind to calmodulin in the presence of Ca2+, with an affinity of 10(6) M-1. The binding of Ca2+ X calmodulin to caldesmon was associated with the neutralization of inhibition of actin-tropomyosin. Ca2+ X calmodulin binding reduced but did not abolish the binding of caldesmon to actin-tropomyosin. From this data we have proposed a model for smooth muscle thin filaments in which Ca2+ regulates activity by converting the inhibited actin-tropomyosin-caldesmon complex to the active complexes, actin-tropomyosin-caldesmon-calmodulin X Ca2+ and actin-tropomyosin.