Component of the DprE1-DprE2 complex that catalyzes the 2-step epimerization of decaprenyl-phospho-ribose (DPR) to decaprenyl-phospho-arabinose (DPA), a key precursor that serves as the arabinose donor required for the synthesis of cell-wall arabinans (PubMed:16291675, PubMed:19299584). DprE1 catalyzes the first step of epimerization, namely FAD-dependent oxidation of the C2' hydroxyl of DPR to yield the keto intermediate decaprenyl-phospho-2'-keto-D-arabinose (DPX) (PubMed:22733761). The intermediate DPX is then transferred to DprE2 subunit of the epimerase complex, most probably through a 'substrate channel' at the interface of DprE1-DprE2 complex (PubMed:25789990). DprE2 then catalyzes the second step of epimerization, the NAD(+)-dependent reduction of DPX that leads to the formation of DPA (PubMed:22733761, PubMed:25789990). Appears to be essential for the growth and survival of M.tuberculosis (PubMed:12657046, PubMed:24517327). NAD(+) + trans,octa-cis-decaprenylphospho-beta-D-arabinofuranose = H(+) + NADH + trans,octa-cis-decaprenylphospho-beta-D-erythro-pentofuranosid-2-ulose Cell wall biogenesis; cell wall polysaccharide biosynthesis. Interacts with DprE1 to form an epimerase complex. Traditional knockout mutant with dprE2 disruption could not be achieved, suggesting this gene is essential (PubMed:24517327). Conditional knock-down mutant of dprE2 show that down-regulation of DprE2 results in growth arrest in vitro (PubMed:24517327). Cells lacking this gene display impaired growth (PubMed:12657046). Was identified as a high-confidence drug target. Belongs to the short-chain dehydrogenases/reductases (SDR) family.