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General Information
the periplasmic nitrate reductase (Nap) from Desulfovibrio desulfuricans belongs to the DMSO reductase family, subfamily I. Classification of Mo-pyranopterin dependent enzymes from the DMSO reductase family, e.g. periplasmic nitrate reductase and formate dehydrogenase, overview. Comparison of the sulfur-shift mechanism in nitrate reductase (Nap) and in formate dehydrogenase (Fdh), detailed overview
Salmonella enterica serovar Typhimurium strains with defects in either nitrate reductase A (narG mutant) or the regulator inducing its transcription in the presence of high concentrations of nitrate (narL mutant) exhibit growth comparable to that of wild-type Salmonella enterica serovar Typhimurium. In contrast, a strain lacking a functional periplasmic nitrate reductase (napA mutant) exhibits a marked growth defect in the lumen of the colon. Inactivation of narP, encoding a response regulator that activates napABC transcription in response to low nitrate concentrations, significantly reduces the growth of Salmonella enterica serovar Typhimurium in the murine host gut lumen
the Salmonella enterica serovar Typhimurium genome contains three nitrate reductases, encoded by the narGHI, narZYV, and napABC genes
physiological function
Salmonella enterica serovar Typhimurium uses the periplasmic nitrate reductase to support its growth on the low nitrate concentrations encountered in the gut, a strategy that may be shared with other enteric pathogens
NapD is a small cytoplasmic protein that is essential for the activity of the periplasmic nitrate reductase and binds tightly to the twinarginine signal peptide of NapA. NapA is structured in its unbound form. The NapA signal peptide undergoes conformational rearrangement upon interaction with NapD. NapA is at least partially folded when bound by its NapD partner. The NapD chaperone binds primarily at the NapA signal peptide in this system and points towards a role for NapD in the insertion of the molybdenum cofactor
physiological function
Escherichia coli is a Gram-negative bacterium that can use nitrate during anaerobic respiration. The catalytic subunit of the involved periplasmic nitrate reductase NapA contains two types of redox cofactor and is exported across the cytoplasmic membrane by the twin-arginine protein transport pathway
genotyping of different strains from M and G populations, overview. The only mutated gene shared between the strains from populations M and G is bll4572, this gene is mutated in all six strains
NasST regulates the nitrate-mediated response of nosZ and napE genes, from the dissimilatory denitrification pathway, regulation of nos and nap genes by the NasST system in the absence of nitrate in mutant strains, overview
modeling of regulation of nap and nos genes by NasST system in Bradyrhizobium japonicum strain USDA110 and nasS and Nos++ mutant strains
the prokaryotic nitrate reductases can be subgrouped as respiratory nitrate reductases (Nar), assimilatory nitrate reductases (Nas), and periplasmic nitrate reductases (Nap). Periplasmic nitrate reductase (Nap) and formate dehydrogenase (Fdh), both belonging to the DMSO reductase family, subfamily I, have a very similar structure, but very different activities. The show key differences that tune them for completely different functions in living cells. Both enzymes share almost identical three-dimensional protein foldings and active sites, in terms of coordination number, geometry and nature of the ligands. The substrates of both enzymes (nitrate and formate) are polyatomic anions that also share similar charge and stereochemistry. In terms of the catalytic mechanism, both enzymes have a common activation mechanism (the sulfur-shift mechanism) that ensures a constant coordination number around the metal ion during the catalytic cycle. In spite of these similarities, they catalyze very different reactions: Nap abstracts an oxygen atom from nitrate releasing nitrite, whereas FdH catalyzes a hydrogen atom transfer from formate and releases carbon dioxide. Detailed comparison, overview. A key difference between the catalytic mechanisms of Nap and FdH is the fact that only Mo is used to reduce nitrate but in Fdhs both Mo and W are catalytically competent to oxidize formate to carbon dioxide
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