Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125.
Proc Natl Acad Sci U S A. 2014 Mar 4;111(9):E817-26. doi: 10.1073/pnas.1401639111. Epub 2014 Feb 18.
Calpains are Ca(2+)-dependent intracellular proteases. We show here that calpain-generated natural C-terminal fragments of proteins that include G protein-coupled receptors, transmembrane ion channels, transcriptional regulators, apoptosis controllers, kinases, and phosphatases (Phe-GluN2a, Lys-Ica512, Arg-Ankrd2, Tyr-Grm1, Arg-Atp2b2, Glu-Bak, Arg-Igfbp2, Glu-IκBα, and Arg-c-Fos), are short-lived substrates of the Arg/N-end rule pathway, which targets destabilizing N-terminal residues. We also found that the identity of a fragment's N-terminal residue can change during evolution, but the residue's destabilizing activity is virtually always retained, suggesting selection pressures that favor a short half-life of the calpain-generated fragment. It is also shown that a self-cleavage of a calpain can result in an N-end rule substrate. Thus, the autoprocessing of calpains can control them by making active calpains short-lived. These and related results indicate that the Arg/N-end rule pathway mediates the remodeling of oligomeric complexes by eliminating protein fragments that are produced in these complexes through cleavages by calpains or other nonprocessive proteases. We suggest that this capability of the Arg/N-end rule pathway underlies a multitude of its previously known but mechanistically unclear functions.
钙蛋白酶是一种依赖 Ca(2+)的细胞内蛋白酶。我们在这里表明，钙蛋白酶生成的包括 G 蛋白偶联受体、跨膜离子通道、转录调节剂、细胞凋亡控制器、激酶和磷酸酶等蛋白质的天然 C 端片段（Phe-GluN2a、Lys-Ica512、Arg-Ankrd2、Tyr-Grm1、Arg-Atp2b2、Glu-Bak、Arg-Igfbp2、Glu-IκBα和 Arg-c-Fos）是 Arg/N 端规则途径的短寿命底物，该途径靶向不稳定的 N 端残基。我们还发现，片段 N 端残基的身份在进化过程中可能会发生变化，但残基的不稳定活性几乎总是保留下来，这表明存在有利于钙蛋白酶生成片段半衰期短的选择压力。研究还表明，钙蛋白酶的自我切割会产生 N 端规则底物。因此，钙蛋白酶的自切割可以通过使活性钙蛋白酶的半衰期变短来控制它们。这些和相关的结果表明，Arg/N 端规则途径通过消除通过钙蛋白酶或其他非程序性蛋白酶在这些复合物中产生的蛋白片段来介导寡聚复合物的重塑。我们认为，Arg/N 端规则途径的这种能力是其先前已知但机制尚不清楚的多种功能的基础。
