Study of cytochrome bo function in Vitreoscilla using a cyo(-) knockout mutant

Vitreoscilla hemoglobin (VHb) overexpression increases hypoxia tolerance in zebrafish (Danio rerio)

Aquaculture farming may benefit from genetically engineering fish to tolerate environmental stress. Here, we used the vector pCVCG expressing the Vitreoscilla hemoglobin (vhb) gene driven by the common carp β-actin promoter to create stable transgenic zebrafish. The survival rate of the 7-day-old F(2) transgenic fish was significantly greater than that of the sibling controls under 2.5% O(2) (dissolved oxygen (DO), 0.91 mg/l). Meanwhile, we investigated the relative expression levels of several marker genes (hypoxia-inducible factor alpha 1, heat shock cognate 70-kDa protein, erythropoietin, beta and alpha globin genes, lactate dehydrogenase, catalase, superoxide dismutase, and glutathione peroxidase) of transgenic fish and siblings after hypoxia exposure for 156 h. The expression profiles of the vhb transgenic zebrafish revealed that VHb could partially alleviate the hypoxia stress response to improve the survival rate of the fish. These results suggest that that vhb gene may be an efficient candidate for genetically modifying hypoxia tolerance in fish.

Evidence that Na+-pumping occurs through the D-channel in Vitreoscilla cytochrome bo

The operon (cyo) encoding the Na(+)-pumping respiratory terminal oxidase (cytochrome bo) of the bacterium Vitreoscilla was transformed into Escherichia coli GV100, a deletion mutant of cytochrome bo. This was done for the wild type operon and five mutants in three conserved Cyo subunit I amino acids known to be crucial for H(+) transport in the E. coli enzyme, one near the nuclear center, one in the K-channel, and one in the D-channel. CO-binding, NADH and ubiquinol oxidase, and Na(+)-pumping activities were all substantially inhibited by each mutation. The wild type Vitreoscilla cytochrome bo can pump Na(+) against a concentration gradient, resulting in a transmembrane concentration differential of 2-3 orders of magnitude. It is proposed that Vitreoscilla cytochrome bo pumps four Na(+) through the D-channel to the exterior and transports four H(+) through the K-channel for the reduction of each O(2).

Proton NMR study of the heme environment in bacterial quinol oxidases

The heme environment and ligand binding properties of two relatively large membrane proteins containing multiple paramagnetic metal centers, cytochrome bo3 and bd quinol oxidases, have been studied by high field proton nuclear magnetic resonance (NMR) spectroscopy. The oxidized bo3 enzyme displays well-resolved hyperfine-shifted 1H NMR resonance assignable to the low-spin heme b center. The observed spectral changes induced by addition of cyanide to the protein were attributed to the structural perturbations on the low-spin heme (heme b) center by cyanide ligation to the nearby high-spin heme (heme o) of the protein. The oxidized hd oxidase shows extremely broad signals in the spectral region where protons near high-spin heme centers resonate. Addition of cyanide to the oxidized bd enzyme induced no detectable perturbations on the observed hyperfine signals, indicating the insensitive nature of this heme center toward cyanide. The proton signals near the low-spin heme b558 center are only observed in the presence of 20% formamide, consistent with a critical role of viscosity in detecting NMR signals of large membrane proteins. The reduced bd protein also displays hyperfine-shifted 1H NMR signals, indicating that the high-spin heme centers (hemes b595 and d) remain high-spin upon chemical reduction. The results presented here demonstrate that structural changes of one metal center can significantly influence the structural properties of other nearby metal center(s) in large membrane paramagnetic metalloproteins.

Sodium ion cycle in bacterial pathogens: evidence from cross-genome comparisons

Analysis of the bacterial genome sequences shows that many human and animal pathogens encode primary membrane Na+ pumps, Na+-transporting dicarboxylate decarboxylases or Na+ translocating NADH:ubiquinone oxidoreductase, and a number of Na+ -dependent permeases. This indicates that these bacteria can utilize Na+ as a coupling ion instead of or in addition to the H+ cycle. This capability to use a Na+ cycle might be an important virulence factor for such pathogens as Vibrio cholerae, Neisseria meningitidis, Salmonella enterica serovar Typhi, and Yersinia pestis. In Treponema pallidum, Chlamydia trachomatis, and Chlamydia pneumoniae, the Na+ gradient may well be the only energy source for secondary transport. A survey of preliminary genome sequences of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Treponema denticola indicates that these oral pathogens also rely on the Na+ cycle for at least part of their energy metabolism. The possible roles of the Na+ cycling in the energy metabolism and pathogenicity of these organisms are reviewed. The recent discovery of an effective natural antibiotic, korormicin, targeted against the Na+ -translocating NADH:ubiquinone oxidoreductase, suggests a potential use of Na+ pumps as drug targets and/or vaccine candidates. The antimicrobial potential of other inhibitors of the Na+ cycle, such as monensin, Li+ and Ag+ ions, and amiloride derivatives, is discussed.