The ThiL enzyme is a valid antibacterial target essential for both thiamine biosynthesis and salvage pathways in Pseudomonas aeruginosa.

: Thiamine pyrophosphate (TPP) is an essential cofactor for various pivotal cellular processes in all living organisms, including bacteria. Thiamine biosynthesis occurs in bacteria but not in humans, so the enzymes in this pathway are attractive targets for antibiotic development. Among these enzymes, thiamine monophosphate kinase (ThiL) catalyzes the final step of this pathway, phosphorylating thiamine monophosphate (TMP) to produce TPP. Here, we extensively investigated ThiL in Pseudomonas aeruginosa, a major pathogen responsible for hospital-acquired infections. We demonstrate that thiL deletion abolishes not only thiamine biosynthesis, but also thiamine salvage capability, and results in growth defects of the ΔthiL strain even in the presence of thiamine derivatives, except for TPP. Most importantly, the pathogenesis of the ΔthiL strain was markedly attenuated compared with wild-type cells, with lower inflammatory cytokine induction and 103-104-fold decreased bacterial load in an in vivo infection model where the intracellular TPP level was in the submicromolar range. To validate P. aeruginosa ThiL (PaThiL) as a drug target, we further characterized its biochemical properties, determining a Vmax of 4.0 ± 0.2 nmol·min-1 and KM values of 111 ± 8 and 8.0 ± 3.5 μM for ATP and TMP, respectively. An in vitro small-molecule screening identified PaThiL inhibitors, including WAY213613, a noncompetitive inhibitor with a Ki value of 13.4 ± 2.3 μM and potential antibacterial activity against P. aeruginosa These comprehensive biological and biochemical results indicate that PaThiL represents a potential drug target for the development of an augmented repertoire of antibiotics against P. aeruginosa.