A protein methyltransferase specific for altered aspartyl residues is important in Escherichia coli stationary-phase survival and heat-shock resistance.
A protein methyltransferase specific for altered aspartyl residues is important in Escherichia coli stationary-phase survival and heat-shock resistance.
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特异针对改变的天冬氨酰残基的蛋白质甲基转移酶对于大肠杆菌的稳定期存活和热激耐受性非常重要。
DOI：
10.1073/pnas.89.20.9885
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发表时间：
1992
影响因子：
11.1
通讯作者：
Clarke,S
中科院分区：
文献类型：
--
作者：
Li,C;Clarke,S
蛋白质会发生自发降解反应，包括天冬酰胺和天冬氨酸残基的脱酰胺、异构化和外消旋。这些反应的主要产物L-异天冬氨酸残基被蛋白质-L-异天冬氨酸(D-天冬氨酸)O-甲基转移酶(EC 2.1.1.77)高度亲和力识别。这种酶催化L-异天冬氨酸残基的甲酯化反应，该反应可以启动其转化为正常的天冬氨酸构型。为了直接研究这种甲基转移酶的生理作用，特别是关于老化蛋白质中异构化的天冬氨酸残基的潜在修复，我们检测了大肠杆菌在缺乏其活性的情况下生存的能力。我们利用基因中断技术，将编码甲基转移酶的pcm基因的染色体拷贝替换为卡那霉素抗性盒，产生了没有检测到L-异天冬氨酸甲基转移酶活性的突变株。虽然没有观察到指数期生长的变化，但pcm-突变体在延长培养到静止期或在55℃的热挑战下不能很好地存活。这些结果为L-异天冬氨酸甲基转移酶在变化的蛋白质代谢中的作用提供了遗传学证据，这些变化的蛋白质可能会在老化的细胞中积累并限制其活性。
Proteins are subject to spontaneous degradation reactions including the deamidation, isomerization, and racemization of asparaginyl and aspartyl residues. A major product of these reactions, the L-isoaspartyl residue, is recognized with high affinity by the protein-L-isoaspartate(D-aspartate) O-methyltransferase (EC 2.1.1.77). This enzyme catalyzes the methyl esterification of the L-isoaspartyl residue in a reaction that can initiate its conversion to the normal aspartyl configuration. To directly study the physiological role of this methyltransferase, especially with respect to the potential repair of isomerized aspartyl residues in aging proteins, we examined the ability of the bacterium Escherichia coli to survive in the absence of its activity. We utilized gene disruption techniques to replace the chromosomal copy of the pcm gene that encodes the methyltransferase with a kanamycin-resistance cassette to produce mutants that have no detectable L-isoaspartyl methyltransferase activity. Although no changes in exponential-phase growth were observed, pcm- mutants did not survive well upon extended culture into stationary phase or upon heat challenge at 55 degrees C. These results provide genetic evidence for a role of the L-isoaspartyl methyltransferase in the metabolism of altered proteins that can accumulate in aging cells and limit their viability.