MANIFESTATIONS OF COOPERATIVE BEHAVIOR IN REGULATED ACTIN FILAMENT DURING ACTIN-ACTIVATED ATP HYDROLYSIS IN PRESENCE OF CALCIUM
MANIFESTATIONS OF COOPERATIVE BEHAVIOR IN REGULATED ACTIN FILAMENT DURING ACTIN-ACTIVATED ATP HYDROLYSIS IN PRESENCE OF CALCIUM
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DOI：
10.1101/sqb.1973.037.01.037
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发表时间：
1973-01-01
期刊：
影响因子：
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通讯作者：
WEBER, A
中科院分区：
文献类型：
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作者：
BREMEL, RD;MURRAY, JM;WEBER, A
在足够的ATP存在下，完整的肌原纤维通过收缩或舒张对周围介质中钙浓度的变化作出反应。肌钙蛋白感知钙的水平，细丝中的肌动蛋白分子要么通过”关闭”，即通过变得无法接近ATP激活的肌球蛋白（Weber和Bremel，1971），使肌动蛋白和肌球蛋白细丝保持彼此分离，要么通过”打开”，即允许收缩发生。肌钙蛋白与原肌球蛋白结合控制肌动蛋白行为的机制尚不清楚。然而，我们知道，受调节的肌动蛋白丝的蛋白质，即含有肌钙蛋白~-原肌球蛋白的蛋白质，被组装成重复单元（Ohtsuki等人，1967; Ebashi等人，1968 a;奥布莱恩等人，1971; Spudich，Huxley，and Finch，in press），由7个肌动蛋白单体、1个原肌球蛋白和1个肌钙蛋白组成（Bremel and Weber，1972）。这些形态单位很可能代表功能实体，正如Ebashi和他的同事几年前首次提出的那样（1968 b）。如果这是正确的，那么我们可以预期在这些单位内蛋白质-蛋白质相互作用。有证据表明，调节肌动蛋白丝的蛋白质之间的合作是存在的。在几个例子中，对单个蛋白质的操作已经显示出改变完整细丝的行为。首先，当从肌钙蛋白中除去钙时（Fuchs和Briggs，1968; Ebashi等人，1968 b）所有的肌动蛋白单体都被”关闭”（Weber和Bremel，1971; Bremel，1972）。第二，当一部分肌动蛋白单体（小于50 μ g/ml）与肌球蛋白在僵直复合物1中结合时，在完全不存在钙的情况下，肌丝中的所有单体都被”打开”（Bremel和Weber，1972; Bremel~ 1972），同时肌钙蛋白对钙的亲和力增加。
In the presence of sufficient ATP intact myofibrils respond to changes in the calcium concentration of the surrounding medium by contracting or relaxing. Troponin senses the level of calcium, and the actin molecules in the thin filament respond either by being" turned off," that is, by becoming inaccessible to ATP-activated myosin (Weber and Bremel, 1971) so that the actin and the myosin filaments remain dissociated from each other, or by being" turned on," that is, by permitting contraction to take place. The mechanism by which troponin in conjunction with tropemyosin controls the behavior of actin is not yet understood. We know, however, that the proteins of the regulated actin filament, ie, containing troponin~-tropomyosin, are assembled into repeating units (Ohtsuki et al., 1967; Ebashi et al., 1968a; O'Brien et al., 1971; Spudich, Huxley, and Finch, in press) consisting of seven actin monomers, one tropomyosin, and one troponin (Bremel and Weber, 1972). It is likely that these morphological units represent functional entities, as first suggested by Ebashi and his colleagues several years ago (1968b). If this is correct, one would expect protein-protein interactions within such units. Evidence for cooperation between proteins of the regulated actin filament does exist. In several instances manipulation of a single protein has been shown to alter the behavior of the complete filament. First, when calcium is removed from troponin (Fuchs and Briggs, 1968; Ebashi et al., 1968b) all of the actin monomers are" turned off"(Weber and Bremel, 1971; Bremel, 1972). Second, when a fraction, less than 50~, of the actin monomers are combined with myosin in rigor complexes 1 all of the monomers in the filament are" turned on" in the complete absence of calcium (Bremel and Weber, 1972; Bremel~ 1972) and at the same time the affinity of troponin for calcium is increased.