Functional interactions between posttranslationally modified amino acids of methyl-coenzyme M reductase in Methanosarcina acetivorans
Functional interactions between posttranslationally modified amino acids of methyl-coenzyme M reductase in Methanosarcina acetivorans
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DOI：
10.1371/journal.pbio.3000507
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发表时间：
2020-02-01
期刊：
影响因子：
9.8
通讯作者：
Metcalf, William W.
中科院分区：
文献类型：
--
作者：
Nayak, Dipti D.;Liu, Andi;Metcalf, William W.
甲基辅酶M还原酶（MCR）通过催化可逆反应在产甲烷古菌和嗜甲烷古菌中产生或消耗这种强效温室气体，在介导全球甲烷水平方面发挥重要作用。在产甲烷古菌中，MCR的α亚基（McrA）通常在活性位点附近含有4至6个后修饰的氨基酸。最近的研究已经确定了酶进行这些修改（硫代甘氨酸和5-[S]-甲基精氨酸），但很少有人知道的形成和功能的剩余postertifictionally修改的残基。在这里，我们提供了在体内的证据表明，一个专门的S-腺苷甲硫氨酸依赖性甲基转移酶编码的基因，我们指定的甲基半胱氨酸修饰（mcmA）是负责形成的S-甲基半胱氨酸在Methanosarcina acetivorans McrA。不能半胱氨酸甲基化的突变体的表型分析表明，S-甲基半胱氨酸残基可能在适应嗜温条件中发挥作用。为了研究S-甲基半胱氨酸残基和先前表征的硫代甘氨酸、5-（S）-甲基精氨酸修饰之间的相互作用，我们产生了M.在所有可能的组合中缺乏三种已知修饰基因的食醋酵母突变体。表型分析揭示了修饰残基之间复杂的生理相关相互作用，其以组合方式改变了MCR的热稳定性，这不易从单个突变体的表型中预测。高分辨率的晶体结构的无活性MCR缺乏修饰的氨基酸是无法区分的完全修饰的酶，这表明，posterionally修饰的残基之间的相互作用不施加的静态结构的酶的主要影响，而是用于微调的活性和效率的MCR。
The enzyme methyl-coenzyme M reductase (MCR) plays an important role in mediating global levels of methane by catalyzing a reversible reaction that leads to the production or consumption of this potent greenhouse gas in methanogenic and methanotrophic archaea. In methanogenic archaea, the alpha subunit of MCR (McrA) typically contains four to six posttranslationally modified amino acids near the active site. Recent studies have identified enzymes performing two of these modifications (thioglycine and 5-[S]-methylarginine), yet little is known about the formation and function of the remaining posttranslationally modified residues. Here, we provide in vivo evidence that a dedicated S-adenosylmethionine-dependent methyltransferase encoded by a gene we designated methylcysteine modification (mcmA) is responsible for formation of S-methylcysteine in Methanosarcina acetivorans McrA. Phenotypic analysis of mutants incapable of cysteine methylation suggests that the S-methylcysteine residue might play a role in adaption to mesophilic conditions. To examine the interactions between the S-methylcysteine residue and the previously characterized thioglycine, 5-(S)-methylarginine modifications, we generated M. acetivorans mutants lacking the three known modification genes in all possible combinations. Phenotypic analyses revealed complex, physiologically relevant interactions between the modified residues, which alter the thermal stability of MCR in a combinatorial fashion that is not readily predictable from the phenotypes of single mutants. High-resolution crystal structures of inactive MCR lacking the modified amino acids were indistinguishable from the fully modified enzyme, suggesting that interactions between the posttranslationally modified residues do not exert a major influence on the static structure of the enzyme but rather serve to fine-tune the activity and efficiency of MCR.