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Helicobacter pylori extracellular proteins are of interest because of possible roles in pathogenesis, host recognition, and vaccine development. We utilized a unique approach by growing two strains (including one nonsequenced strain) in a defined serum-free medium and directly analyzing the proteins present in the culture supernatants by LC-MS/MS. Over 125 proteins were identified in the extracellular proteomes of two H. pylori strains. Forty-five of these proteins were enriched in the extracellular fraction when compared to soluble cell-associated protein samples. Our analysis confirmed and expanded on the previously reported H. pylori extracellular proteome. Extracellular proteins of interest identified here included cag pathogenicity island protein Cag24 (CagD); proteases HP0657 and HP1012; a polysaccharide deacetylase, HP0310, possibly involved in the hydrolysis of acetyl groups from host N-acetylglucosamine residues or from residues on the cell surface; and HP0953, an uncharacterized protein that appears to be restricted to Helicobacter species that colonize the gastric mucosa. In addition, our analysis found eight previously unidentified outer membrane proteins and two lipoproteins that could be important cell surface proteins.

Several accessory proteins are required for the maturation of two nickel-containing enzymes in the gastric pathogen Helicobacter pylori. These two enzymes are hydrogenase and urease. Among the accessory/maturation proteins, the nickel-binding HypA protein has been previously shown to be required for the full activity of both the hydrogenase and the urease enzymes, while another nickel-binding protein, UreE, is known to be solely involved in the urease maturation process. In this study, UreE was shown to be required under all nickel levels for full activation of the apourease. By use of cross-linking studies, an interaction between purified HypA and UreE proteins was identified, leading to the formation of a 34 kDa heterodimer complex. The cross-linked adduct was detected by immunoblotting with either anti-HypA or anti-UreE antiserum. By using a two-plasmid system in Escherichia coli, the highest urease activity was achieved under low nickel conditions only when the UreE protein was expressed along with the wild-type HypA protein, but not with its nickel-binding-deficient variant HypA H2A. Addition of only 1 microM NiCl(2) into minimal medium abolished the need for HypA to activate the urease. Although various attempts to show direct nickel transfer from HypA to UreE failed, these results suggest that interactions between the nickel-binding accessory proteins HypA and UreE are required to allow nickel transfer from HypA eventually to the apourease in H. pylori.

Background Helicobacter pylori colonizes the human stomach and is the etiological agent of peptic ulcer disease. All three H. pylori strains that have been sequenced to date contain a potential operon whose products share homology with the subunits of acetone carboxylase (encoded by acxABC) from Xanthobacter autotrophicus strain Py2 and Rhodobacter capsulatus strain B10. Acetone carboxylase catalyzes the conversion of acetone to acetoacetate. Genes upstream of the putative acxABC operon encode enzymes that convert acetoacetate to acetoacetyl-CoA, which is metabolized further to generate two molecules of acetyl-CoA. Results To determine if the H. pylori acxABC operon has a role in host colonization the acxB homolog in the mouse-adapted H. pylori SS1 strain was inactivated with a chloramphenicol-resistance (cat) cassette. In mouse colonization studies the numbers of H. pylori recovered from mice inoculated with the acxB:cat mutant were generally one to two orders of magnitude lower than those recovered from mice inoculated with the parental strain. A statistical analysis of the data using a Wilcoxin Rank test indicated the differences in the numbers of H. pylori isolated from mice inoculated with the two strains were significant at the 99% confidence level. Levels of acetone associated with gastric tissue removed from uninfected mice were measured and found to range from 10–110 μmols per gram wet weight tissue. Conclusion The colonization defect of the acxB:cat mutant suggests a role for the acxABC operon in survival of the bacterium in the stomach. Products of the H. pylori acxABC operon may function primarily in acetone utilization or may catalyze a related reaction that is important for survival or growth in the host. H. pylori encounters significant levels of acetone in the stomach which it could use as a potential electron donor for microaerobic respiration.

Despite research into the nutritional requirements of Helicobacter pylori , little is known regarding its use of complex substrates, such as peptides. Analysis of genome sequences revealed putative ABC-type transporter genes for dipeptide ( dppABCDF ) and oligopeptide ( oppABCD ) transport. Genes from each system were PCR amplified, cloned, and disrupted by cassette insertion either individually ( dppA, dppB, dppC, oppA, oppB , and oppC ) or to create double mutants ( dppA oppA, dppB oppB, dppB dppC , and oppB oppC ). Peptide-utilizing abilities of the strains were assessed by monitoring growth in a chemically defined medium where the only source of the essential amino acid isoleucine was from peptides of various lengths (two to nine amino acids long). The dipeptide system mutants lacked the ability to use certain dipeptides, hexapeptides, and nonapeptides. However, these mutants retained some ability to grow with other dipeptides, tripeptides, and tetrapeptides. Of the oligopeptide mutants, only the oppB strain differed significantly from the wild type. This strain showed a wild-type phenotype for growth with longer peptides (hexa- and nonapeptides) while having a decreased ability to utilize di-, tri-, and tetrapeptides. The dppA oppA and dppB oppB mutants showed similar phenotypes to those of the dppA and dppB mutants, respectively. Peptide digestion by metalloproteases was ruled out as the cause for residual peptide transport by growing mutant strains in the presence of either EDTA or EGTA. Degradation products associated with a fluorescein isothiocyanate-labeled hexapeptide (plus cells) were minimal. An as yet unidentified peptide transport system(s) in H. pylori is proposed to be responsible for the residual transport.

The original genome annotation of the hyperthermophilic archaeon Pyrococcus furiosus contained 2,065 open reading frames (ORFs). The genome was subsequently automatically annotated in two public databases by the Institute for Genomic Research (TIGR) and the National Center for Biotechnology Information (NCBI). Remarkably, more than 500 of the originally annotated ORFs differ in size in the two databases, many very significantly. For example, more than 170 of the predicted proteins differ at their N termini by more than 25 amino acids. Similar discrepancies were observed in the TIGR and NCBI databases with the other archaeal and bacterial genomes examined. In addition, the two databases contain 60 (NCBI) and 221 (TIGR) ORFs not present in the original annotation of P. furiosus . In the present study we have experimentally assessed the validity of 88 previously unannotated ORFs. Transcriptional analyses showed that 11 of 61 ORFs examined were expressed in P. furiosus when grown at either 95 or 72°C. In addition, 7 of 54 ORFs examined yielded heat-stable recombinant proteins when they were expressed in Escherichia coli , although only one of the seven ORFs was expressed in P. furiosus under the growth conditions tested. It is concluded that the P. furiosus genome contains at least 17 ORFs not previously recognized in the original annotation. This study serves to highlight the discrepancies in the public databases and the problems of accurately defining the number and sizes of ORFs within any microbial genome.

The hyperthermophilic archaeon, Pyrococcus furiosus , was grown on maltose near its optimal growth temperature, 95°C, and at the lower end of the temperature range for significant growth, 72°C. In addition, cultures were shocked by rapidly dropping the temperature from 95 to 72°C. This resulted in a 5-h lag phase, during which time little growth occurred. Transcriptional analyses using whole-genome DNA microarrays representing 2,065 open reading frames (ORFs) in the P. furiosus genome showed that cells undergo three very different responses at 72°C: an early shock (1 to 2 h), a late shock (5 h), and an adapted response (occurring after many generations at 72°C). Each response involved the up-regulation in the expression of more than 30 ORFs unique to that response. These included proteins involved in translation, solute transport, amino acid biosynthesis, and tungsten and intermediary carbon metabolism, as well as numerous conserved-hypothetical and/or membrane-associated proteins. Two major membrane proteins were evident after one-dimensional sodium dodecyl sulfate-gel analysis of cold-adapted cells, and staining revealed them to be glycoproteins. Their cold-induced expression evident from the DNA microarray analysis was confirmed by quantitative PCR. Termed CipA (PF0190) and CipB (PF1408), both appear to be solute-binding proteins. While the archaea do not contain members of the bacterial cold shock protein (Csp) family, they all contain homologs of CipA and CipB. These proteins are also related phylogenetically to some cold-responsive genes recently identified in certain bacteria. The Cip proteins may represent a general prokaryotic-type cold response mechanism that is present even in hyperthermophilic archaea.

Rubrerythrin was purified by multistep chromatography under anaerobic, reducing conditions from the hyperthermophilic archaeon Pyrococcus furiosus . It is a homodimer with a molecular mass of 39.2 kDa and contains 2.9 ± 0.2 iron atoms per subunit. The purified protein had peroxidase activity at 85°C using hydrogen peroxide with reduced P. furiosus rubredoxin as the electron donor. The specific activity was 36 μmol of rubredoxin oxidized/min/mg with apparent K m values of 35 and 70 μM for hydrogen peroxide and rubredoxin, respectively. When rubrerythrin was combined with rubredoxin and P. furiosus NADH:rubredoxin oxidoreductase, the complete system used NADH as the electron donor to reduce hydrogen peroxide with a specific activity of 7.0 μmol of H 2 O 2 reduced/min/mg of rubrerythrin at 85°C. Strangely, as-purified (reduced) rubrerythrin precipitated when oxidized by either hydrogen peroxide, air, or ferricyanide. The gene (PF1283) encoding rubrerythrin was expressed in Escherichia coli grown in medium with various metal contents. The purified recombinant proteins each contained approximately three metal atoms/subunit, ranging from 0.4 Fe plus 2.2 Zn to 1.9 Fe plus 1.2 Zn, where the metal content of the protein depended on the metal content of the E. coli growth medium. The peroxidase activities of the recombinant forms were proportional to the iron content. P. furiosus rubrerythrin is the first to be characterized from a hyperthermophile or from an archaeon, and the results are the first demonstration that this protein functions in an NADH-dependent, hydrogen peroxide:rubredoxin oxidoreductase system. Rubrerythrin is proposed to play a role in the recently defined anaerobic detoxification pathway for reactive oxygen species.