Structure of an as(III) S -adenosylmethionine methyltransferase: Insights into the mechanism of arsenic biotransformation

A. Abdul Ajees, Kavitha Marapakala, Charles Packianathan, Banumathi Sankaran, Barry P. Rosen

Research output: Contribution to journalArticlepeer-review

106 Citations (Scopus)


Enzymatic methylation of arsenic is a detoxification process in microorganisms but in humans may activate the metalloid to more carcinogenic species. We describe the first structure of an As(III) S-adenosylmethionine methyltransferase by X-ray crystallography that reveals a novel As(III) binding domain. The structure of the methyltransferase from the thermophilic eukaryotic alga Cyanidioschyzon merolae reveals the relationship between the arsenic and S-adenosylmethionine binding sites to a final resolution of ∼1.6 Å. As(III) binding causes little change in conformation, but binding of SAM reorients helix α4 and a loop (residues 49-80) toward the As(III) binding domain, positioning the methyl group for transfer to the metalloid. There is no evidence of a reductase domain. These results are consistent with previous suggestions that arsenic remains trivalent during the catalytic cycle. A homology model of human As(III) S-adenosylmethionine methyltransferase with the location of known polymorphisms was constructed. The structure provides insights into the mechanism of substrate binding and catalysis.

Original languageEnglish
Pages (from-to)5476-5485
Number of pages10
Issue number27
Publication statusPublished - 10-07-2012

All Science Journal Classification (ASJC) codes

  • Biochemistry


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