Aerobic glycerol dissimilation via the Enterococcus faecalis DhaK pathway depends on NADH oxidase and a phosphotransfer reaction from PEP to DhaK via EIIADha

Two pathways for glycerol dissimilation are present in Enterococcus faecalis. Either glycerol is first phosphorylated by glycerol kinase and then oxidized by glycerol-3-phosphate oxidase with molecular oxygen as the electron acceptor (GlpO/GlpK pathway), or it is first oxidized by glycerol dehydrogenase with NAD⁺ as the acceptor of the reduction equivalents and then phosphorylated by dihydroxyacetone kinase (GldA/DhaK pathway). The final end product in both cases is dihydroxyacetone phosphate (DHAP). The genes of the GldA/DhaK pathway are present in a four-gene operon structure encoding GldA, a small hypothetical protein (EF1359), and two subunits of dihydroxyacetone kinase (DhaK and DhaL). We demonstrate in this study that protein EF1359 is part of a phosphorylation cascade which phosphorylates dihydroxyacetone in a phosphoenolpyruvate (PEP)-dependent reaction via EI, HPr, EF1359 and DhaLK. Furthermore we show that aerobic dissimilation of glycerol via the GldA/DhaK pathway is dependent on active NADH oxidase to regenerate NADH in Ent. faecalis. A refined model of the aerobic metabolism of glycerol via the GldA/DhaK pathway is presented.