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Structure of an As(III) S-Adenosylmethionine Methyltransferase: Insights into the Mechanism of Arsenic Biotransformation

Ajees, Abdul A (2012) Structure of an As(III) S-Adenosylmethionine Methyltransferase: Insights into the Mechanism of Arsenic Biotransformation. Biochemistry, 51. pp. 5476-5485.

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Abstract

ABSTRACT: 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- enosylmethionine 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 Sadenosylmethionine 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) Sadenosylmethionine methyltransferase with the location of known polymorphisms was constructed. The structure provides insights into the mechanism of substrate binding and catalysis.

Item Type: Article
Subjects: Departments at MU > Atomic Molecular Physics
Depositing User: KMC Manipal
Date Deposited: 11 Jul 2013 04:15
Last Modified: 11 Jul 2013 04:15
URI: http://eprints.manipal.edu/id/eprint/136510

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