A DIRECT REGULATORY ROLE FOR TROPONIN-T AND A DUAL ROLE FOR TROPONIN-C IN THE CA2+ REGULATION OF MUSCLE-CONTRACTION
A DIRECT REGULATORY ROLE FOR TROPONIN-T AND A DUAL ROLE FOR TROPONIN-C IN THE CA2+ REGULATION OF MUSCLE-CONTRACTION
复制标题
DOI：
10.1074/jbc.270.6.2557
复制
发表时间：
1995-02-10
影响因子：
4.8
通讯作者：
ZHAO, JJ
中科院分区：
文献类型：
--
作者：
POTTER, JD;SHENG, ZL;ZHAO, JJ
肌钙蛋白（Tn）由钙结合（TnC）、抑制性（TnI）和原肌球蛋白结合（TnT）三个亚基组成，在脊椎动物横纹肌收缩的钙调节中起重要作用。这三个亚基通过彼此相互作用以及与其他细丝蛋白相互作用来发挥功能。以前的研究表明，TnT的主要作用是通过与TnI和原肌球蛋白的相互作用，将TnI.TnC复合物锚在细丝上。我们在这里提出了一个新的作用TnT。我们的研究结果表明，当TnT与TnI.TnC复合物结合时，有一个激活的肌动球蛋白ATP酶是Ca ~（2+）依赖性的。为了确定后者是由TnC对TnT的直接作用引起还是由TnC对传递给TnT的TnI的作用间接引起，我们制备了TnI的缺失突变体（缺失残基1-57），TnI（d57）（Sheng等，（1992）J. Biol. Chem.267，25407-25413），其与TnC相互作用而不与TnT相互作用。野生型（TnI.TnC.TnT）和突变型（TnI（d57）.Tnc.TnT）Tn复合物在Ca ~（2+）调节肌动球蛋白-S1 ATP酶活性方面表现出相当的活性。同样，TnT和TnI（d57）可以同样地重建TnI耗尽的皮肤肌纤维。因此，由于TnI（d57）不与TnT相互作用，这些结果表明TnT通过与TnC直接相互作用重建天然Ca 2+敏感性。因此，Ca 2+与TnC的结合具有双重作用：1）释放TnI对ATP酶的抑制，2）通过与TnT的相互作用激活ATP酶。
Troponin (Tn), containing three subunits: Ca2+ binding (TnC), inhibitory (TnI), and tropomyosin binding (TnT), plays a crucial role in the Ca2+ regulation of vertebrate striated muscle contraction. These three subunits function by interacting with each other and with the other thin filament proteins. Previous studies suggested that the primary role of TnT is to anchor the TnI.TnC complex to the thin filament, primarily through its interactions with TnI and tropomyosin. We propose here a new role for TnT. Our results indicate that, when TnT is combined with the TnI.TnC complex, there is an activation of actomyosin ATPase that is Ca2+-dependent. To determine whether the latter results from a direct effect of TnC on TnT or indirectly from an effect of TnC on TnI which is transmitted to TnT, we prepared a deletion mutant (deletion of residues 1-57) of TnI, TnI(d57) (Sheng et al. (1992) J. Biol. Chem. 267, 25407-25413), which interacts with TnC but not TnT. Both wild type (TnI.TnC.TnT) and mutant (TnI(d57).Tnc.TnT) Tn complexes demonstrated equivalent activity in the Ca2+ regulation of actomyosin-S1 ATPase activity. Similarly, both TnT and TnI(d57) could equally reconstitute TnI-depleted skinned muscle fibers. Therefore, since TnI(d57) does not interact with TnT, these results suggest that TnT reconstitutes native Ca2+ sensitivity via direct interaction with TnC. Thus Ca2+ binding to TnC would have a dual role: 1) release of the ATPase inhibition by TnI and 2) activation of the ATPase through interaction with TnT.