Pyridoxal-5'-phosphate (the active form of vitamin B6) is an essential cofactor in many enzymatic reactions. While animals lack any of the pathways for de novo synthesis and salvage of vitamin B6, it is synthesized by two distinct biosynthetic routes in bacteria, fungi, parasites, and plants. One of them is the PdxA/PdxJ pathway found in the gamma subdivision of proteobacteria. It depends on the pdxB gene, which encodes erythronate-4-phosphate dehydrogenase (PdxB), a member of the d-isomer specific 2-hydroxyacid dehydrogenase superfamily. Erythronate-4-phosphate dehydrogenase is a homodimeric enzyme, and each subunit it made up of three domains. This entry represents the C-terminal dimerisation domain which consists of two beta-strands and four alpha-helices PMID:17217963.