Science, 2016, 351, 507-510
An unprecedented mechanism of nucleotide methylation in organisms containing thyX
Tatiana V. Mishanina,1 Liping Yu,2Kalani Karunaratne,1 Dibyendu Mondal,1 John M. Corcoran,1Michael A. Choi,1Amnon Kohen1†
1Department of Chemistry, University of Iowa, Iowa City, IA52242, USA.
2Nuclear Magnetic Resonance (NMR) Core Facility and Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
†Corresponding author. E-mail: firstname.lastname@example.org
Abstract: In several human pathogens, thyX-encoded flavin-dependent thymidylate synthase (FDTS) catalyzes the last step in the biosynthesis of thymidylate, one of the four DNA nucleotides. ThyX is absent in humans, rendering FDTS an attractive antibiotic target; however, the lack of mechanistic understanding prohibits mechanism-based drug design. Here, we report trapping and characterization of two consecutive intermediates, which together with previous crystal structures indicate that the enzyme’s reduced flavin relays a methylene from the folate carrier to the nucleotide acceptor. Furthermore, these results corroborate an unprecedented activation of the nucleotide that involves no covalent modification but only electrostatic polarization by the enzyme’s active site. These findings indicate a mechanism that is very different from thymidylate biosynthesis in humans, underscoring the promise of FDTS as an antibiotic target.