Phosphorylation specificities of protein kinase C isozymes for bovine cardiac troponin I and troponin T and sites within these proteins and regulation of myofilament properties
Phosphorylation specificities of protein kinase C isozymes for bovine cardiac troponin I and troponin T and sites within these proteins and regulation of myofilament properties
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DOI：
10.1074/jbc.271.38.23277
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发表时间：
1996-09-20
影响因子：
4.8
通讯作者：
Kuo, JF
中科院分区：
文献类型：
--
作者：
Jideama, NM;Noland, TA;Kuo, JF
蛋白激酶 C (PKC) 同工酶 α、δ、ε 和 zeta 在成年大鼠心肌细胞中表达，在磷酸化牛心肌肌钙蛋白复合物中的肌钙蛋白 I 和肌钙蛋白 T 亚基时表现出不同的底物特异性，因此，由于它们具有不同的底物亲和力，PKC-α、-δ 和 -ε 磷酸化肌钙蛋白 I 的程度高于肌钙蛋白 T，但相反，PKC-zeta 对后者的磷酸化程度高于前者。此外，PKC 同工酶在磷酸化这些蛋白质中作为游离亚基或肌钙蛋白复合物中的不同位点方面表现出离散的特异性。与其他同工酶不同，PKC-delta 能够独特地磷酸化肌钙蛋白 I 中的 Ser-23/Ser-24，这是蛋白激酶 A (PKA) 的真正磷酸化位点；因此，与 PKA 一样，它降低了重构肌动球蛋白 S-1 的 Ca2+ 刺激的 MgATP 酶的 Ca2+ 敏感性。此外，与 PKC-α 一样，PKC-δ 很容易磷酸化 Ser-43/Ser-45（所有 PKC 同工酶共有的位点）并降低 MgATP 酶的最大活性。在这方面，PKC-δ 充当 PKC-α 和 PKA 的杂合体。与 PKC-α、-δ 和 -ε 相比，PKC-zeta 专门磷酸化肌钙蛋白 T 中两个以前未知的位点。PKC-α 磷酸化肌钙蛋白 T 导致 Ca2+ 敏感性和最大活性降低，而 PKC-zeta 磷酸化导致 Ca2+ 敏感性轻微增加，但不影响 MgATPase 的最大活性。肌钙蛋白 I 和肌钙蛋白 T 在成年大鼠心肌细胞中得到原位证实。本研究首次证明 PKC 同工酶对心肌中两种生理底物的磷酸化具有明显的特异性，并产生功能性后果。
Protein kinase C (PKC) isozymes alpha, delta, epsilon, and zeta, shown to be expressed in adult rat cardiomyocytes, displayed distinct substrate specificities in phosphorylating troponin I and troponin T subunits in the bovine cardiac troponin complex, Thus, because they have different substrate affinities, PKC-alpha, -delta, and -epsilon phosphorylated troponin I more than troponin T, but PKC-zeta conversely phosphorylated the latter more than the former, Furthermore, PKC isozymes exhibited discrete specificities in phosphorylating distinct sites in these proteins as free subunits or in the troponin complex, Unlike other isozymes, PKC-delta was uniquely able to phosphorylate Ser-23/Ser-24 in troponin I, the bona fide phosphorylation sites for protein kinase A (PKA); and consequently, like PKA, it reduced Ca2+ sensitivity of Ca2+-stimulated MgATPase of reconstituted actomyosin S-1. In addition, PKC-delta, like PKC-alpha, readily phosphorylated Ser-43/Ser-45 (sites common for all PKC isozymes) and reduced maximal activity of MgATPase, In this respect, PKC-delta functioned as a hybrid of PKC-alpha and PKA. In contrast to PKC-alpha, -delta, and -epsilon, PKC-zeta exclusively phosphorylated two previously unknown sites in troponin T. Phosphorylation of troponin T by PKC-alpha resulted in decreases in both Ca2+ sensitivity and maximal activity, whereas phosphorylation by PKC-zeta resulted in a slight increase of the Ca2+ sensitivity without affecting the maximal activity of MgATPase, Most of the in vitro phosphorylation sites in troponin I and troponin T were confirmed in situ in adult rat cardiomyocytes.The present study has demonstrated for the first time distinct specificities of PKC isozymes for phosphorylation of two physiological substrates in the myocardium, with functional consequences.