Genetic evidence that genes fdhD and fdhE do not control synthesis of formate dehydrogenase-N in Escherichia coli K-12

Abstract

Enterobacteria synthesize two formate dehydrogenases, formate dehydrogenase-N (encoded byfdnGHI) and formate dehydrogenase H (encoded by fdhF). Previous work has identified two rha-linked Salmonella typhimurium genes, fdnB and fdnC, which are required primarily for formate dehydrogenase-N activity. Analogous mutants, termed fdhD and fdhE, have been isolated in Escherichia coli. We used gene fusions betweenfdnG, the structural gene for the large subunit of formate dehydrogenase-N, and lacZ, the structural gene for I-galactosidase, to examine E. coli fdnGHI operon expression in fdhD and fdhE insertion mutants. Expression of the 4'(fdnG-lacZ) gene fusions was little affected by these insertions, suggesting that fdhD and fdhE do not control transcription or UGA decoding of the formate dehydrogenase-N structural genes. Our complementation tests, with cloned E. coli fdhD and fdhE genes, indicate that the S. typhimurium fdnC and fdnB genes are functionally homologous to the E. coli fdhD and fdhE genes, respectively.Formate (HCO2-) is a product of anaerobic pyruvate cleavage. Enterobacteria have two pathways for anaerobic metabolism of formate (Fig. 1). A respiratory pathway, formate-nitrate oxidoreductase, allows for energy conservation via oxidative phosphorylation during anaerobic growth. This pathway involves two membrane-bound, multisubunit enzymes, formate dehydrogenase-N (FDH-N) and respiratory nitrate reductase. Synthesis of this enzyme complex is induced by nitrate during anaerobic growth. FDH-N and respiratory nitrate reductase are associated with specific cytochromes, cyt bId' and cyt bNa,j, respectively. The strongly electronegative redox potential of the C02-HCO2-couple (Eo' = -432 mV) makes formate an efficient electron donor for respiratory nitrate reduction. The second pathway, formate-hydrogen lyase, operates anaerobically in the absence of nitrate. This pathway involves two enzymes, formate dehydrogenase-H (FDH-H) and hydrogenase 3. Synthesis of this enzyme complex is induced by anaerobiosis only in the absence of nitrate. The exact physiological role of formate-hydrogen lyase is not established. The H2 and CO2 produced by formate-hydrogen lyase accumulates in Durham tubes, so gas production provides a qualitative estimate of this activity. Formate metabolism in enterobacteria has been recently reviewed (33).The three subunits of FDH-N are encoded by the fdnGHI operon at 32 min on the Escherichia coli genetic map (5). The FDH-H polypeptide is encoded by the fdhF gene at 92 min on the E. coli map (27). The FdnG and FdhF polypeptides each contain selenium in the form of selenocysteine, and each associates with molybdenum cofactor. Thus, mutants defective in selenocysteine (sel) or molybdenum cofactor (chl) synthesis or incorporation are devoid of formate dehydrogenase activity (for reviews, see references 7 and 33).Analysis of E. coli and Salmonella typhimurium has identified four sel genes (originally termed fdh), lesions in which abolish the activities of 20,24). The selA (80 min) and selD (38 min) gen...

Expression and characterization of the Escherichia coli fdo locus and a possible physiological role for aerobic formate dehydrogenase

“…This observation correlates with the failure to detect any FDH-N polypeptides in fdhE mutants by rocket immunoelectrophoresis (30). Our results show clearly that neither fdhD nor fdhE lesions affect fdo expression (Table 5), in parallel with previous work from Stewart and coworkers giving evidence that fdhD and fdhE do not control transcription of fdn (48). Taken together, these data support the idea that the FdhD and FdhE proteins act at the posttranslational level to ensure the correct processing or assembly of both respiratory FDH isoenzymes.…”

“…The fdhD and fdhE genes encode accessory proteins which are required for the formation of both respiratory FDH isoenzymes in an active form (36,42,48) while the selAB operon has been shown to be involved in selenium incorporation as a selenocysteine to produce the three FDHs in a functional state (10,41). Whatever the mutation tested (Table 5, rows 8, 9, 12, and 13), the pattern of expression of the fdo-uidA fusion did not show any significant change.…”

A Sulfurtransferase Is Essential for Activity of Formate Dehydrogenases in Escherichia coli

“…In addition to TusA and IscU, large-scale interactome studies identified FdhD as a binding partner of IscS (7,8). FdhD has been shown to be required for the activity of formate dehydrogenases (FDHs) 2 in E. coli through an unknown mechanism (9,10). E. coli synthesizes three FDHs that decompose formate to carbon dioxide and protons.…”

Corynebacterium glutamicum harbours a molybdenum cofactor-dependent formate dehydrogenase which alleviates growth inhibition in the presence of formate

“…In E. coli, FdhD was found to be essential for activity of the two respiratory FDHs FDH-N and FDH-O as well as for the fermentative FDH-H (Abaibou et al, 1995;Schlindwein et al, 1990;Stewart et al, 1991). Recently, FdhD from E. coli was shown to interact with IscS, one of the three E. coli L-cysteine desulfurases (Thomé et al, 2012).…”