Insight into the catalytic mechanism of thymidylate synthase ThyX of Campylobacter jejuni

International audienceFor de novo synthesis of the essential DNA precursor dTMP, Campylobacter jejuni uses a novel thymidylate synthase, named ThyX (1). Different from canonical dimeric thymidylate synthase ThyA, ThyX is a flavoprotein and an active tetramer that utilizes NADPH as reducing agent, methylenetetrahydrofolate as methyl donor and dUMP as methyl acceptor. Its proposed catalytic mechanism starts with the oxidation of NADPH, followed by methylation of dUMP. ThyX proteins and human ThyA are unrelated in terms of sequence and structure, and use different catalytic mechanisms, making the essential ThyX enzymes interesting antimicrobial targets

Two distinct pathways for thymidylate (dTMP) synthesis in (hyper)thermophilic bacteria and archaea

International audienceThe hyperthermophilic anaerobic archaeon Pyrococcus obyssi, which lacks thymidine kinase, incorporates label from extracellular uracil, but not from thymidine, into its DNA. This implies that P. obyssi must synthesize dTMP (thymidylate), an essential precursor for DNA synthesis, de novo. However, iterative similarity searches of the three completed Pyrococcus genomes fail to detect candidate genes for canonical thymidylate synthase ThyA, suggesting the presence of alternative pathways for dTMP synthesis. Indeed, by identifying a novel class of flavin-dependent thymidylate synthases, ThyX, we have recently proven that two distinct pathways for de novo synthesis of dTMP are operational in the microbial world. While both thyX and thyA can be found in hyperthermophilic micro-organisms, the phylogenetic distribution of thyX among hyperthermophiles is wider than that of thyA. In this contribution, we discuss the differences in the distinct mechanisms of dTMP synthesis, with a special emphasis on hyperthermophilic micro-organisms