Genetic Analysis Using Vitamin B-6 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 B-6 metabolism, including its integration with other biological pathways, are not fully understood. In this study, we examined the metabolic perturbations caused by the vitamin B-6 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 B-6 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 B-6 antagonist that is often used to mimic vitamin B-6 deficiency and to study PLP-dependent enzyme kinetics. In addition to de novo PLP biosynthesis, we define a metabolic connection between vitamin B-6 metabolism and synthesis of thiamine and CoA. This work provides a foundation for the use of dPN to study vitamin B-6 metabolism in other organisms.