title: Identification and characterization of arsenite methyltransferase from an archaeon, Methanosarcina acetivorans C2A.
abstract: Arsenic is a ubiquitous toxic contaminant in the environment. The methylation of arsenic can affect its toxicity and is primarily mediated by biological processes. Few studies have focused on the mechanism of arsenic methylation in archaea although archaea are widespread in the environment. Here, an arsenite [As(III)] methyltransferase (ArsM) was identified and characterized from an archaeon Methanosarcina acetivorans C2A. Heterologous expression of MaarsM was shown to confer As(III) resistance to an arsenic-sensitive strain of E. coli through arsenic methylation and subsequent volatilization. Purified MaArsM protein was further identified the function in catalyzing the formation of various methylated products from As(III) in vitro. Methylation of As(III) by MaArsM is highly dependent on the characteristics of the thiol cofactors used, with some of them (coenzyme M, homocysteine, and dithiothreitol) more efficient than GSH. Site-directed mutagenesis demonstrated that three conserved cysteine (Cys) residues (Cys62, Cys150, and Cys200) in MaArsM were necessary for As(III) methylation, of which only Cys150 and Cys200 were required for the methylation of monomethylarsenic. These results present a molecular pathway for arsenic methylation in archaea and provide some insight into the role of archaea in As biogeochemistry.
authors.affiliation: State Key Lab of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, People's Republic of China.
authors.forename: Pei-Pei
authors.initials: PP
authors.lastname: Wang
authors.forename: Guo-Xin
authors.initials: GX
authors.lastname: Sun
authors.forename: Yong-Guan
authors.initials: YG
authors.lastname: Zhu
mesh_terms: D001151:Arsenic / Q000378:metabolism; D001711:Biotransformation; D003001:Cloning, Molecular; D017124:Conserved Sequence; D003545:Cysteine / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D019766:Genes, Archaeal; D005978:Glutathione / Q000378:metabolism; D008658:Inactivation, Metabolic; D017020:Methanosarcina / Q000201:enzymology* / Q000235:genetics; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014835:Volatilization
chemical_list: D013438:Sulfhydryl Compounds; D012436:S-Adenosylmethionine; D008780:Methyltransferases; C116338:arsenite methyltransferase; D005978:Glutathione; D003545:Cysteine; D001151:Arsenic