Genetic Analysis Using Vitamin B6 Antagonist 4-Deoxypyridoxine Uncovers a Connection between Pyridoxal 5'-Phosphate and Coenzyme A Metabolism in Salmonella enterica.

Pyridoxal 5'-phosphate (PLP) is an essential cofactor for organisms in all three domains of life. Despite the central role of PLP, many aspects of vitamin B6 metabolism, including its integration with other biological pathways, are not fully understood. In this study, we examined the metabolic perturbations caused by the vitamin B6 antagonist 4-deoxypyridoxine (dPN) in a ptsJ mutant of Salmonella enterica serovar Typhimurium LT2. Our data suggest that PdxK (pyridoxal/pyridoxine/pyridoxamine kinase [EC 2.7.1.35]) phosphorylates dPN to 4-deoxypyridoxine 5'-phosphate (dPNP), which in turn can compromise the de novo biosynthesis of PLP. The data are consistent with the hypothesis that accumulated dPNP inhibits GlyA (serine hydroxymethyltransferase [EC 2.1.2.1]) and/or GcvP (glycine decarboxylase [EC 1.4.4.2]), two PLP-dependent enzymes involved in the generation of one-carbon units. Our data suggest that this inhibition leads to reduced flux to coenzyme A (CoA) precursors and subsequently decreased synthesis of CoA and thiamine. This study uncovers a link between vitamin B6 metabolism and the biosynthesis of CoA and thiamine, highlighting the integration of biochemical pathways in microbes. IMPORTANCE PLP is a ubiquitous cofactor required by enzymes in diverse metabolic networks. The data presented here expand our understanding of the toxic effects of dPN, a vitamin B6 antagonist that is often used to mimic vitamin B6 deficiency and to study PLP-dependent enzyme kinetics. In addition to de novo PLP biosynthesis, we define a metabolic connection between vitamin B6 metabolism and synthesis of thiamine and CoA. This work provides a foundation for the use of dPN to study vitamin B6 metabolism in other organisms.