Methylation in Antibiotic Biosynthesis: Methylcobalamin-Radical SAM Enzymes

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I have obtained B. Sc. in chemistry from University of Belgrade, Serbia and Montenegro, in 2000, and Ph. D. in organic chemistry from University of Illinois at Urbana-Champaign in May 2005. During graduate studies, I have developed new methods for the chemoselective carbohydrate-peptide ligations under the joint guidance of Professors David Y. Gin and Wilfred A. van der Donk. Currently, I am a Damon Runyon Cancer Research Foundation postdoctoral fellow in the laboratory of Professor Christopher T. Walsh at Harvard Medical School. HMS and Professor Walsh are providing an outstanding research environment and are committed to the success of the postdoctoral fellows. My postdoctoral research is focused on the characterization of a recently discovered class of nonheme Fe (II) halogenases, capable of carrying out halogenation of unactivated carbon centers. Thus far, we have reconstituted halogenation activity in the barbamide system. In this study, we demonstrated that the triple chlorination of the unactivated methyl group of the carrier-protein tethered L-leucine substrate is mediated by the tandem action of two nonheme Fell halogenases, BarB1 and BarB2. I am currently investigating mechanistic aspects of halogenation of unactivated carbon centers through the investigation of pre-steady state kinetic parameters and EPR and Mossbauer investigation of metal center during the catalysis. The objective of the proposed project is mechanistic description of methylcobalamin-radical SAM enzymes that carry out methylations of sp2 carbon centers in antibiotic biosynthesis. Our goal is to understand the logic that nature uses to channel methylcobalamin, iron-sulfur clusters and deoxyadenosyl radicals to perform this novel carbon-carbon bond formation in enzymology. The methylation event will be studied in the context of generation of the 5-methylpyrrole-2-carboxylate pharmacophore in aminocoumarin antibiotic biosynthesis, and hydroxyethyl side chain in the biosynthesis of beta lactam antibiotic thienamycin. Better understanding of enzymes involved in the antibiotic biosynthesis can lead to the development of new antibiotic variants through combinatorial biosynthesis. This is especially important because of the development of bacterial resistance to commonly used antibiotics.