Bacillus sp. CX-1砷甲基化的分子机制研究

微生物介导的砷甲基化是砷生物地球化学循环的重要组成部分，对环境中砷的形态转化及毒性产生重要影响，因而研究其发生的机制具有重要的环境意义。目前，微生物体内仅发现了一类催化砷甲基化的酶，名为As(III)-S-腺苷甲硫氨酸甲基转移酶（ArsM）。已报道的ArsMs都有四个保守的半胱氨酸位点（Cys），它们的存在被认为是ArsMs发挥活性的一个必要条件。有趣的是，申请人近期在菌株Bacillus sp. CX-1中鉴定到一个ArsM的同源蛋白（BlArsM），仅有三个保守的Cys，但仍有甲基化As(III)的能力。本项目中，我们将进一步阐明BlArsM对于As(III)的解毒作用及催化机制，以验证它是否是一个新型的ArsM。此外，前期的研究结果表明，菌株CX-1中应该还存在另外一个未知的As(III)甲基转移酶，本项目将继续寻找这个未知的酶并研究其作用机制，以期深入解析菌株砷甲基化的分子机制。

Microbial arsenic (As) methylation is an important component of the As biogeochemical cycle. Microbial methylation transforms the chemical species of As and its toxicity in the environment. Understanding the mechanism of microbial As methylation is therefore of great environmental importance. Until now, arsenite S-adenosylmethionine methyltransferase (ArsM) is found to be the only class of enzymes involved in microbial As methylation. It has been reported that all ArsMs studied to date contain four conserved cysteine residues, which are essential for the methylation activity. Recently, we have identified an ArsM homologous protein (BlArsM) from a Bacillus strain named CX-1. Interestingly, BlArsM has only three conserved cysteine residues, but still has the activity of As(III) methylation. In this proposal, we will investigate the detoxification and catalytic mechanism of BlArsM to verify if BlArsM represents a new type of ArsM. Furthermore, our preliminary work showed that there must exist another unknown As(III) methyltransferase in this bacterium. In this proposal, we will identify the unknown As(III) methyltransferase and investigate its mechanism of As methylation. The research proposed in the project will aim to elucidate the molecular mechanisms of As methylation by Bacillus sp. CX-1.