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首页> 外文期刊>Biochemistry >Identification of Catalytic Residues in the As(III) S-Adenosylmethionine Methyltransferase
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Identification of Catalytic Residues in the As(III) S-Adenosylmethionine Methyltransferase

机译：鉴定As（III）S-腺苷甲硫氨酸甲基转移酶中的催化残基

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摘要

The enzyme As(III) S-adenosylmethionine methyltransferase (EC 2.1.1.137) (ArsM or AS3MT) is found in members of every kingdom, from bacteria to humans. In these enzymes, there are three conserved cysteine residues at positions 72, 174, and 224 in the CmArsM orthologue from the thermophilic eukaryotic alga Cyanidioschyzon sp. 5508. Substitution of any of the three led to loss of As(III) methylation. In contrast, a C72A mutant still methylated trivalent methylarsenite [MAs(III)]. Protein fluorescence of a single-tryptophan mutant reported binding of As(III) or MAs(III). As(GS)_3 and MAs(GS)2 bound significantly faster than As(III), suggesting that the glutathionylated arsenicals are preferred substrates for the enzyme. Protein fluorescence also reported binding of Sb(III), and the purified enzyme methylated and volatilized Sb(III). The results suggest that all three cysteine residues are necessary for the first step in the reaction, As(III) methylation, but that only Cys174 and Cys224 are required for the second step, methylation of MAs(III) to dimethylarsenite [DMAs(III)]. The rate-limiting step was identified as the conversion of DMAs(III) to trimethylarsine, and DMAs(III) accumulates as the principal product.
机译：从细菌到人类，在每个王国的成员中都发现了As（III）S-腺苷甲硫氨酸甲基转移酶（EC 2.1.1.137）（ArsM或AS3MT）。在这些酶中，来自嗜热真核藻类Cyanidioschyzon sp。的CmArsM直系同源物的72、174和224位有三个保守的半胱氨酸残基。 5508.替换这三个中的任何一个都导致As（III）甲基化的损失。相反，C72A突变体仍甲基化三价甲基亚砷酸盐[MAs（III）]。单色氨酸突变体的蛋白质荧光报告了As（III）或MAs（III）的结合。 As（GS）_3和MAs（GS）2的结合速度明显快于As（III），这表明谷胱甘肽化的砷是该酶的优选底物。蛋白质荧光还报道了Sb（III）的结合，纯化的酶甲基化并挥发了Sb（III）。结果表明，反应的第一步中所有三个半胱氨酸残基都是必需的，即As（III）甲基化，而第二步，即将MAs（III）甲基化为二甲基亚砷酸盐[DMAs（III）]，则仅需要Cys174和Cys224。 ]。限速步骤被确定为DMAs（III）向三甲基tri的转化，并且DMAs（III）积累为主要产物。

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