CRBM, Université Montpellier 2 and 1, CNRS UMR 5237, Montpellier 34293, France.
Cell. 2010 Nov 12;143(4):564-78. doi: 10.1016/j.cell.2010.10.014.
Polyglutamylation is a posttranslational modification that generates glutamate side chains on tubulins and other proteins. Although this modification has been shown to be reversible, little is known about the enzymes catalyzing deglutamylation. Here we describe the enzymatic mechanism of protein deglutamylation by members of the cytosolic carboxypeptidase (CCP) family. Three enzymes (CCP1, CCP4, and CCP6) catalyze the shortening of polyglutamate chains and a fourth (CCP5) specifically removes the branching point glutamates. In addition, CCP1, CCP4, and CCP6 also remove gene-encoded glutamates from the carboxyl termini of proteins. Accordingly, we show that these enzymes convert detyrosinated tubulin into Δ2-tubulin and also modify other substrates, including myosin light chain kinase 1. We further analyze Purkinje cell degeneration (pcd) mice that lack functional CCP1 and show that microtubule hyperglutamylation is directly linked to neurodegeneration. Taken together, our results reveal that controlling the length of the polyglutamate side chains on tubulin is critical for neuronal survival.
多聚谷氨酸化是一种翻译后修饰，它在微管蛋白和其他蛋白质上产生谷氨酸侧链。虽然已经证明这种修饰是可逆的，但对于催化去谷氨酸化的酶知之甚少。在这里，我们描述了胞质羧肽酶（CCP）家族成员催化蛋白去谷氨酸化的酶促机制。三种酶（CCP1、CCP4 和 CCP6）催化多聚谷氨酸链的缩短，第四种酶（CCP5）专门去除分支点谷氨酸。此外，CCP1、CCP4 和 CCP6 还从蛋白质的羧基末端去除基因编码的谷氨酸。因此，我们表明这些酶将去酪氨酸化的微管蛋白转化为Δ2-微管蛋白，并修饰其他底物，包括肌球蛋白轻链激酶 1。我们进一步分析了缺乏功能性 CCP1 的小脑浦肯野细胞退化（pcd）小鼠，并表明微管蛋白的高谷氨酸化与神经退行性变直接相关。总之，我们的结果表明，控制微管蛋白上多聚谷氨酸侧链的长度对神经元的存活至关重要。
