The PDXB is a small subfamily that includes a group of bacterial enzymes found in ɣ-proteobacteria and Bacteroidetes, including biochemically studied PdxB from E. coli (PDXB_ECOLI). PdxB oxidizes 4-phospho-ᴅ-erythronate to 2-keto-3-hydroxy-4-phosphobutanoate and uses various 2-keto acids as cosubstrates, utilizing NAD as a cofactor. The reaction is the second step in the biosynthesis of pyridoxal phosphate — active form of vitamin B6. Uniquely for 2HADHs, PDXB family proteins have two consecutive proline residues within the βB-αD loop, which are spatially conserved in all the crystal structures of PDXB proteins. Another unique feature of PDXB is presence of a C-terminal dimerization domain.