Purification and characterization of the oxidase from the marine bacterium Pseudomonas nautica 617

Influence of Cupric (Cu2+) Ions on the Iron Oxidation Mechanism by DNA-Binding Protein from Starved Cells (Dps) from Marinobacter nauticus

Dps proteins (DNA-binding proteins from starved cells) are multifunctional stress defense proteins from the Ferritin family expressed in Prokarya during starvation and/or acute oxidative stress. Besides shielding bacterial DNA through binding and condensation, Dps proteins protect the cell from reactive oxygen species by oxidizing and storing ferrous ions within their cavity, using either hydrogen peroxide or molecular oxygen as the co-substrate, thus reducing the toxic effects of Fenton reactions. Interestingly, the interaction between Dps and transition metals (other than iron) is a known but relatively uncharacterized phenomenon. The impact of non-iron metals on the structure and function of Dps proteins is a current topic of research. This work focuses on the interaction between the Dps from Marinobacter nauticus (a marine facultative anaerobe bacterium capable of degrading petroleum hydrocarbons) and the cupric ion (Cu²⁺), one of the transition metals of greater biological relevance. Results obtained using electron paramagnetic resonance (EPR), Mössbauer and UV/Visible spectroscopies revealed that Cu²⁺ ions bind to specific binding sites in Dps, exerting a rate-enhancing effect on the ferroxidation reaction in the presence of molecular oxygen and directly oxidizing ferrous ions when no other co-substrate is present, in a yet uncharacterized redox reaction. This prompts additional research on the catalytic properties of Dps proteins.

The roles of Rhodobacter sphaeroides copper chaperones PCu(A)C and Sco (PrrC) in the assembly of the copper centers of the aa(3)-type and the cbb(3)-type cytochrome c oxidases

The α proteobacter Rhodobacter sphaeroides accumulates two cytochrome c oxidases (CcO) in its cytoplasmic membrane during aerobic growth: a mitochondrial-like aa(3)-type CcO containing a di-copper Cu(A) center and mono-copper Cu(B), plus a cbb(3)-type CcO that contains Cu(B) but lacks Cu(A). Three copper chaperones are located in the periplasm of R. sphaeroides, PCu(A)C, PrrC (Sco) and Cox11. Cox11 is required to assemble Cu(B) of the aa(3)-type but not the cbb(3)-type CcO. PrrC is homologous to mitochondrial Sco1; Sco proteins are implicated in Cu(A) assembly in mitochondria and bacteria, and with Cu(B) assembly of the cbb(3)-type CcO. PCu(A)C is present in many bacteria, but not mitochondria. PCu(A)C of Thermus thermophilus metallates a Cu(A) center in vitro, but its in vivo function has not been explored. Here, the extent of copper center assembly in the aa(3)- and cbb(3)-type CcOs of R. sphaeroides has been examined in strains lacking PCu(A)C, PrrC, or both. The absence of either chaperone strongly lowers the accumulation of both CcOs in the cells grown in low concentrations of Cu(2+). The absence of PrrC has a greater effect than the absence of PCu(A)C and PCu(A)C appears to function upstream of PrrC. Analysis of purified aa(3)-type CcO shows that PrrC has a greater effect on the assembly of its Cu(A) than does PCu(A)C, and both chaperones have a lesser but significant effect on the assembly of its Cu(B) even though Cox11 is present. Scenarios for the cellular roles of PCu(A)C and PrrC are considered. The results are most consistent with a role for PrrC in the capture and delivery of copper to Cu(A) of the aa(3)-type CcO and to Cu(B) of the cbb(3)-type CcO, while the predominant role of PCu(A)C may be to capture and deliver copper to PrrC and Cox11. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes.

Interaction of bd-type quinol oxidase from Escherichia coli and carbon monoxide: heme d binds CO with high affinity

Comparative studies on the interaction of the membrane-bound and detergent-solubilized forms of the enzyme in the fully reduced state with carbon monoxide at room temperature have been carried out. CO brings about a bathochromic shift of the heme d band with a maximum at 644 nm and a minimum at 624 nm, and a peak at 540 nm. In the Soret band, CO binding to cytochrome bd results in absorption decrease and minima at 430 and 445 nm. Absorption perturbations in the Soret band and at 540 nm occur in parallel with the changes at 630 nm and reach saturation at 3-5 microM CO. The peak at 540 nm is probably either beta-band of the heme d-CO complex or part of its split alpha-band. In both forms of cytochrome bd, CO reacts predominantly with heme d. Addition of high CO concentrations to the solubilized cytochrome bd results in additional spectral changes in the gamma-band attributable to the reaction of the ligand with 10-15% of low-spin heme b558. High-spin heme b595 does not bind CO even at high concentrations of the ligand. The apparent dissociation constant values for the heme d-CO complex of the membrane-bound and detergent-solubilized forms of the fully reduced enzyme are about 70 and 80 nM, respectively.

Construction of gene engineered hE/293 cells continuously releasing human endostatin

AIM: To express the recombinant eukaryotic expression vector containing human endostatin gene in human embryonic kidney HEK293 cells, and construct a cell line continuously secreting human endostatin (hES).

METHODS: Human endostatin cDNA containing interleukin-2 (IL-2) secreting peptide was cloned into eukaryotic expression plasmid pSNA2 to construct the recombinant plasmid pSNA2/endostatin. The plasmid pSNA2/endostatin was transfected into HEK293 cells by cationic liposome. The positive cell clones were selected by G418 and then named hE/293 cells. The expression of endostatin protein was analyzed by Western blot. The release of biologically active endostatin was confirmed using assays of ECV304 proliferation and the angiogenesis experiment of chicken chorioallantoic membrane (CAM).

RESULTS: Enzyme digestion and sequence analysis confirmed that the eukaryotic expression vector pSNA2/endostatin had been successfully constructed. After G418 selection, 3 strains of cells stably expressing hES were obtained, named as hE/293 cells. Western blot showed that ES protein with a molecular weight of 20 kDa existed in the supernatant of hE/293 cells. No endostatin expression was found in the control cells. The assays of ECV304 proliferation showed that the supernatant of hE/293 cells inhibited ECV304 cell proliferation induced by basic fibroblast growth factor in comparison with that of HEK29 cells (48 h: 0.125 ± 0.007 vs 0.159 ± 0.020, P < 0.01; 72 h: 0.088 ± 0.016 vs 0.249 ± 0.070, P < 0.01). There were fewer blood vessels in the CAM treated with ES protein.

CONCLUSION: Target cell line hE/293 is successfully constructed which it can stably secret hES protein, inhibit the ECV304 cell proliferation and CAM angiogenesis.

Cytochrome c oxidase as a proton-pumping peroxidase: reaction cycle and electrogenic mechanism

Cytochrome oxidase (COX) is considered to integrate in a single enzyme two consecutive mechanistically different redox activities--oxidase and peroxidase--that can be catalyzed elsewhere by separate hemoproteins. From the viewpoint of energy transduction, the enzyme is essentially a proton pumping peroxidase with a built-in auxiliary eu-oxidase module that activates oxygen and prepares in situ H2O2, a thermodynamically efficient but potentially hazardous electron acceptor for the proton pumping peroxidase. The eu-oxidase and peroxidase phases of the catalytic cycle may be performed by different structural states of COX. Resolution of the proton pumping peroxidase activity of COX and identification of individual charge translocation steps inherent in this reaction are discussed, as well as the specific role of the two input proton channels in proton translocation.

Purification and properties of cytochrome bo-type ubiquinol oxidase from a marine bacterium Vibrio alginolyticus

Ubiquinol oxidase was extracted from membranes of a marine bacterium Vibrio alginolyticus with a nonionic detergent Liponox DCH and was purified about 130-fold by DEAE-Sephacel, DEAE-5PW and Sephacryl S-300. The purified ubiquinol oxidase was composed of three subunits with apparent M(r) of 79, 36 and 13 kDa on SDS-polyacrylamide gel electrophoresis. The oxidase contained cytochrome b, cytochrome o and copper atoms. The presence of heme O was confirmed by reverse-phase HPLC analysis. Ubiquinol-1, duroquinol and tetramethylphenylene diamine, but not horse heart reduced cytochrome c, were oxidized by this enzyme. The oxidase required no salts for activity and was stimulated by several detergents and by diphosphatidyl glycerol. The activity was strongly inhibited by KCN, 2-n-heptyl-4-hydroxyquinoline N-oxide and ZnSO4. These properties were essentially similar to those of cytochrome bo-type ubiquinol oxidase from Escherichia coli, suggesting that the bo-type ubiquinol oxidase is functioning as a proton pump in the marine V. alginolyticus.

Reduction of carbon monoxide to formaldehyde by the terminal oxidase of the marine bacterium Pseudomonas nautica strain 617

When exposed to CO, the aerobic respiratory system of the marine bacterium Pseudomonas nautica strain 617, previously reduced with dithionite, undergoes reoxidation. When dealing with the purified oxidase (dithionite reduced) exposure of the enzyme to CO induces its reoxidation (collapse of its alpha band). Under our experimental conditions, this form of the oxidase could not be reduced again by dithionite. Addition of formaldehyde to the native oxidized enzyme resulted in full inhibition of the oxidase reduction by dithionite, presumably due to complex formation. We hypothesized a reduction of CO into formaldehyde and a locking of the active site by the reaction product. By using flash photolysis, it was possible to turn over the enzyme, accumulate the reaction product and identify it as formaldehyde. When using the membrane-bound enzyme, formaldehyde accumulated without the help of flash photolysis. This unusual reduction of CO to formaldehyde could be related to the previously reported uncommon features of the P. nautica oxidase, in particular O2 reduction into H2O2 as end product [(1989) FEBS Lett. 247, 475-479].