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Arsenic methylation by a novel ArsM As(III) S ‐adenosylmethionine methyltransferase that requires only two conserved cysteine residues
Author(s) -
Huang Ke,
Xu Yan,
Packianathan Charles,
Gao Fan,
Chen Chuan,
Zhang Jun,
Shen Qirong,
Rosen Barry P.,
Zhao FangJie
Publication year - 2018
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13882
Subject(s) - cysteine , methylation , methyltransferase , biology , biochemistry , serine , conserved sequence , methionine , heterologous expression , enzyme , microbiology and biotechnology , amino acid , gene , peptide sequence , recombinant dna
Summary Arsenic (As) biomethylation is an important component of the As biogeochemical cycle that can influence As toxicity and mobility in the environment. Biomethylation of As is catalyzed by the enzyme arsenite (As[III]) S ‐adenosylmethionine methyltransferase (ArsM). To date, all identified ArsM orthologs with As(III) methylation activities have four conserved cysteine residues, which are thought to be essential for As(III) methylation. Here, we isolated an As(III)‐methylating bacterium, Bacillus sp. CX‐1, and identified a gene encoding a S ‐adenosylmethionine methyltranserase termed BlArsM with low sequence similarities (≤ 39%) to other ArsMs. BlArsM has six cysteine residues (Cys10, Cys11, Cys145, Cys193, Cys195 and Cys268), three of which (Cys10, Cys145 and Cys195) align with conserved cysteine residues found in most ArsMs. BlarsM is constitutively expressed in Bacillus sp. CX‐1. Heterologous expression of BlarsM conferred As(III) resistance. Purified BlArsM methylated both As(III) and methylarsenite (MAs[III]), with a final product of dimethylarsenate (DMAs[V]). When all six cysteines were individually altered to serine residues, only C145S and C195S derivatives lost the ability to methylate As(III) and MAs(III). The derivative C10S/C11S/C193S/C268S was still active. These results suggest that BlArsM is a novel As(III) S ‐adenosylmethionine methyltransferase requiring only two conserved cysteine residues. A model of As(III) methylation by BlArsM is proposed.