4'-Deoxypyridoxine disrupts vitamin B₆ homeostasis in Escherichia coli K12 through combined inhibition of cumulative B₆ uptake and PLP-dependent enzyme activity

Pyridoxal 5'-phosphate (PLP) is the active form of vitamin B₆ and a cofactor for many essential metabolic processes such as amino acid biosynthesis and one carbon metabolism. 4'-deoxypyridoxine (4dPN) is a long known B₆ antimetabolite but its mechanism of action was not totally clear. By exploring different conditions in which PLP metabolism is affected in the model organism Escherichia coli K12, we showed that 4dPN cannot be used as a source of vitamin B₆ as previously claimed and that it is toxic in several conditions where vitamin B₆ homeostasis is affected, such as in a B₆ auxotroph or in a mutant lacking the recently discovered PLP homeostasis gene, yggS. In addition, we found that 4dPN sensitivity is likely the result of multiple modes of toxicity, including inhibition of PLP-dependent enzyme activity by 4'-deoxypyridoxine phosphate (4dPNP) and inhibition of cumulative pyridoxine (PN) uptake. These toxicities are largely dependent on the phosphorylation of 4dPN by pyridoxal kinase (PdxK).