Corynebacterium glutamicum uses the Embden-Meyerhof-Parnas pathway of glycolysis and gains 2 mol of ATP per mol of glucose by substrate-level phosphorylation (SLP). To engineer glycolysis without net ATP formation by SLP, endogenous phosphorylating NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was replaced by nonphosphorylating NADPdependent glyceraldehyde-3-phosphate dehydrogenase (GapN) from Clostridium acetobutylicum, which irreversibly converts glyceraldehyde-3-phosphate (GAP) to 3-phosphoglycerate (3-PG) without generating ATP. As shown recently (S. Takeno, R. Murata, R. Kobayashi, S. Mitsuhashi, and M. Ikeda, Appl Environ Microbiol 76:7154 -7160, 2010, http://dx.doi.org/10.1128/AEM.01464-10), this ATP-neutral, NADPH-generating glycolytic pathway did not allow for the growth of Corynebacterium glutamicum with glucose as the sole carbon source unless hitherto unknown suppressor mutations occurred; however, these mutations were not disclosed. In the present study, a suppressor mutation was identified, and it was shown that heterologous expression of udhA encoding soluble transhydrogenase from Escherichia coli partly restored growth, suggesting that growth was inhibited by NADPH accumulation. Moreover, genome sequence analysis of second-site suppressor mutants that were able to grow faster with glucose revealed a single point mutation in the gene of non-proton-pumping NADH:ubiquinone oxidoreductase (NDH-II) leading to the amino acid change D213G, which was shared by these suppressor mutants. Since related NDH-II enzymes accepting NADPH as the substrate possess asparagine or glutamine residues at this position, D213G, D213N, and D213Q variants of C. glutamicum NDH-II were constructed and were shown to oxidize NADPH in addition to NADH. Taking these findings together,
ATP-neutral glycolysis by the replacement of endogenous NAD-dependent GAPDH with NADP-dependent GapN became possible via oxidation of NADPH formed in this pathway by mutant NADPH-accepting NDH-II D213G and thus by coupling to electron transport phosphorylation (ETP).A TP generation occurs naturally by substrate-level phosphorylation (SLP), electron transport phosphorylation (ETP), photophosphorylation, and decarboxylation phosphorylation. The Embden-Meyerhof-Parnas (EMP) pathway of glycolysis supplies ATP by SLP in the absence of terminal electron acceptors or anaerobic conditions, as well as supplying direct precursors for biomass formation (1). Bacteria and archaea possess one or more of multiple biologically feasible routes for glucose catabolism, such as the EMP pathway, the Entner-Doudoroff (ED) pathway, and the phosphoketolase pathway, which yield zero to 3 ATP molecules per glucose molecule and exist in different variants. In natural habitats, a trade-off between the rate and the yield of ATP production is observed for heterotrophic organisms; faster but less efficient ATP production may be advantageous under conditions characterized by a low abundance of growth substrates (2, 3). For example, Zymomonas mobilis ferments suga...