The Bacillus subtilis yqjI gene encodes the NADP+-dependent 6-P-gluconate dehydrogenase in the pentose phosphate pathway.
Despite the importance of the oxidative pentose phosphate (PP) pathway as a major source of reducing power and metabolic intermediates for biosynthetic processes, almost no direct genetic or biochemical evidence is available for Bacillus subtilis. Using a combination of knockout mutations in known and putative genes of the oxidative PP pathway and 13C-labeling experiments, we demonstrated that yqjI encodes the NADP+-dependent 6-P-gluconate dehydrogenase, as was hypothesized previously from sequence similarities. Moreover, YqjI was the predominant isoenzyme during glucose and gluconate catabolism, and its role in the oxidative PP pathway could not be played by either of two homologues, GntZ and YqeC. This conclusion is in contrast to the generally held view that GntZ is the relevant isoform; hence, we propose a new designation for yqjI, gndA, the monocistronic gene encoding the principal 6-P-gluconate dehydrogenase. Although we demonstrated the NAD+-dependent 6-P-gluconate dehydrogenase activity of GntZ, gntZ mutants exhibited no detectable phenotype on glucose, and GntZ did not contribute to PP pathway fluxes during growth on glucose. Since gntZ mutants grew normally on gluconate, the functional role of GntZ remains obscure, as does the role of the third homologue, YqeC. Knockout of the glucose-6-P dehydrogenase-encoding zwf gene was primarily compensated for by increased glycolytic fluxes, but about 5% of the catabolic flux was rerouted through the gluconate bypass with glucose dehydrogenase as the key enzyme.
Zamboni
Nicola
N
Institute of Biotechnology, ETH Zürich, Zürich, Switzerland.
Fischer
Eliane
E
Laudert
Dietmar
D
Aymerich
Stéphane
S
Hohmann
Hans-Peter
HP
Sauer
Uwe
U
D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000201:enzymology* / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002250:Carbon Radioisotopes / Q000378:metabolism; D017124:Conserved Sequence; D017353:Gene Deletion; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005942:Gluconates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D042843:Glucose 1-Dehydrogenase / Q000235:genetics / Q000378:metabolism; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009249:NADP / Q000378:metabolism; D010427:Pentose Phosphate Pathway / Q000235:genetics*; D010734:Phosphogluconate Dehydrogenase / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D002250:Carbon Radioisotopes; D005942:Gluconates; D007527:Isoenzymes; D009249:NADP; D010734:Phosphogluconate Dehydrogenase; D042843:Glucose 1-Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D005947:Glucose; C030691:gluconic acid