Moody C J, Marston S B, Smith C W
FEBS Lett. 1985 Oct 21;191(1):107-12. doi: 10.1016/0014-5793(85)81003-6.
Ca2+-sensitive thin filaments from vascular smooth muscle were disassembled into their constituent proteins, actin, tropomyosin and caldesmon. Caldesmon bound to both actin and to actin-tropomyosin and inhibited actin-tropomyosin activation of skeletal muscle myosin MgATPase. It also promoted the aggregation of actin or actin-tropomyosin into parallel aligned bundles. Quantitative electron microscopy measurements showed that with 1.1 microM actin-tropomyosin, 1.6 +/- 0.5% (n = 3) of the filaments were in bundles. At 0.073 microM, caldesmon inhibited MgATPase activity by 50%, whereas bundling was 3.0 +/- 1.3% (n = 4). At 0.37 microM caldesmon, MgATPase inhibition was 83% while 28.1 +/- 6.9% (n = 4) of filaments were in bundles. Experiments at 4.4 microM in which MgATPase and bundling were measured in the same samples gave similar results. Small bundles of 2-3 filaments showed the most frequent occurrence at 1.1 microM actin. At 4.4 microM actin the most common bundle size was 3-5 filaments, with the occasional occurrence of large bundles consisting of up to 120 filaments. The incidence of bundling was the same in the presence and absence of tropomyosin. Thus caldesmon can induce the formation of actin bundles but this property bears no relationship to its inhibition of MgATPase activity.
来自血管平滑肌的钙敏感细肌丝被分解为其组成蛋白，即肌动蛋白、原肌球蛋白和钙调蛋白。钙调蛋白既与肌动蛋白结合，也与肌动蛋白 - 原肌球蛋白复合物结合，并抑制骨骼肌肌球蛋白MgATP酶的肌动蛋白 - 原肌球蛋白激活。它还促进肌动蛋白或肌动蛋白 - 原肌球蛋白聚集成平行排列的束状结构。定量电子显微镜测量表明，在含有1.1微摩尔肌动蛋白 - 原肌球蛋白的情况下，1.6±0.5%（n = 3）的细丝呈束状。在钙调蛋白浓度为0.073微摩尔时，其对MgATP酶活性的抑制率为50%，而束状结构形成率为3.0±1.3%（n = 4）。当钙调蛋白浓度为0.37微摩尔时，MgATP酶抑制率为83%，而28.1±6.9%（n = 4）的细丝呈束状。在4.4微摩尔浓度下对同一样品进行MgATP酶活性和束状结构形成的测量实验，得到了类似的结果。在1.1微摩尔肌动蛋白浓度下，最常见的是由2 - 3根细丝组成的小束状结构。在4.4微摩尔肌动蛋白浓度下，最常见的束状结构大小为3 - 5根细丝，偶尔会出现由多达120根细丝组成的大束状结构。在有或没有原肌球蛋白存在的情况下，束状结构形成的发生率是相同的。因此，钙调蛋白可以诱导肌动蛋白束的形成，但这种特性与其对MgATP酶活性的抑制作用无关。
