GenK-Catalyzed C-6鈥?Methylation in the Biosynthesis of Gentamicin: Isolation and Characterization of a Cobalamin-Dependent Radical SAM Enzyme

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• 作者：Hak Joong Kim ; Reid M. McCarty ; Yasushi Ogasawara ; Yung-nan Liu ; Steven O. Mansoorabadi ; Jake LeVieux ; Hung-wen Liu
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：June 5, 2013
• 年：2013
• 卷：135
• 期：22
• 页码：8093-8096
• 全文大小：343K
• 年卷期：v.135,no.22(June 5, 2013)
• ISSN：1520-5126

文摘

The existence of cobalamin (Cbl)-dependent enzymes that are members of the radical S-adenosyl-l-methionine (SAM) superfamily was previously predicted on the basis of bioinformatic analysis. A number of these are Cbl-dependent methyltransferases, but the details surrounding their reaction mechanisms have remained unclear. In this report we demonstrate the in vitro activity of GenK, a Cbl-dependent radical SAM enzyme that methylates an unactivated sp³ carbon during the biosynthesis of gentamicin, an aminoglycoside antibiotic. Experiments to investigate the stoichiometry of the GenK reaction revealed that 1 equiv each of 5鈥?deoxyadenosine and S-adenosyl-homocysteine are produced for each methylation reaction catalyzed by GenK. Furthermore, isotope-labeling experiments demonstrate that the S-methyl group from SAM is transferred to Cbl and the aminoglycoside product during the course of the reaction. On the basis of these results, one mechanistic possibility for the GenK reaction can be ruled out, and further questions regarding the mechanisms of Cbl-dependent radical SAM methyltransferases, in general, are discussed.