Structural comparison of urease and a GroEL analog from Helicobacter pylori

Traditional and Modern Diagnostic Approaches in Diagnosing Pediatric Helicobacter pylori Infection

Helicobacter pylori (H. pylori) is the most common bacterial infection worldwide, is usually acquired during childhood and is related to gastric carcinogenesis during adulthood. Therefore, its early proper diagnosis and subsequent successful eradication represent the cornerstones of gastric cancer prevention. The aim of this narrative review was to assess traditional and modern diagnostic methods in terms of H. pylori diagnosis. Several invasive and non-invasive methods were described, each with its pros and cons. The invasive diagnostic methods comprise endoscopy with biopsy, rapid urease tests, histopathological exams, cultures and biopsy-based molecular tests. Among these, probably the most available, accurate and cost-effective test remains histology, albeit molecular tests definitely remain the most accurate despite their high costs. The non-invasive tests consist of urea breath tests, serology, stool antigens and non-invasive molecular tests. Urea breath tests and stool antigens are the most useful in clinical practice both for the diagnosis of H. pylori infection and for monitoring the eradication of this infection after therapy. The challenges related to accurate diagnosis lead to a choice that must be based on H. pylori virulence, environmental factors and host peculiarities.

Helicobacter pylori infection in children: an overview of diagnostic methods

Children differ from adults regarding Helicobacter pylori (H. pylori) infection in many terms. H. pylori infection represents a key factor in the pathogenesis of duodenal ulcer and chronic gastritis in children. H. pylori infection causes some extraintestinal diseases as well as gastrointestinal diseases. Although, among these illnesses in children, symptoms like recurrent abdominal pain are not specific. Moreover, the role of the pathogen in the growth faltering, iron deficiency anemia, and asthma still remains controversial. A reliable method to detect H. pylori infection is a crucial issue, sand is still a matter of active debate. The tests applied for H. pylori diagnosis are grouped as either invasive or non-invasive methods. Invasive methods consist of endoscopic evaluation, the rapid urease test (RUT), histology, and bacterial culture. Non-invasive tests include the urea breath test (UBT), stool antigen test (SAT), serology, and molecular diagnostic approaches. Use of endoscopy is a pre-requisite for all invasive methods and poses difficulties in children as it is a difficult procedure and requires patient's cooperation. For this reason, the non-invasive tests have been commonly used in children, although their accuracy is not very reliable in some cases. Invasive tests may be opted to confirm the diagnosis as and when needed. This review presents the diagnostic tests used to detect H. pylori infection in children.

Mechanistic Insight Into the Interaction Between Helicobacter pylori Urease Subunit α and Its Molecular Chaperone Hsp60

Helicobacter pylori is the etiologic agent in a variety of gastroduodenal diseases. As its key pathogenic factors, both urease and Hsp60 play important roles in the pathogenesis of H. pylori. Previous studies have suggested that there is close relationship between urease and Hsp60, which implied that Hsp60 may act as a chaperone in urease stabilization and assembly. However, how these two proteins interact remains unclear. In this study, the impact of Hsp60 on urease activity of H. pylori lysate was first detected to confirm the interaction between urease and Hsp60. Pull-down assays further indicated that Hsp60 could bind to UreA subunit but not UreB. Then, the 3D structure of Hsp60 was modeled using I-TASSER to simulate the binding complex with UreA by molecular docking. The results showed that UreA is a perfect fit for the cavity of Hsp60. Analysis of the resulting model demonstrated that at least seven residues of UreA, located on two interfaces, participate in the interaction. Site-directed mutagenesis of these potential residues showed reduced affinity with Hsp60 than the wild type UreA through surface plasmon resonance (SPR) experiments, and D68 appears to have an important role in the affinity. Further analysis also showed that mutation of E25 and K26 caused a more rapid association and dissociation than with wild UreA, implying that they have roles in stabilizing the interaction complex. These affinity comparisons suggested that the interfaces predicted by molecular docking are credible. Our study indicated a direct interaction between Hsp60 and urease and revealed the binding interfaces and key residues involved in the interaction. These results provide further evidence for the chaperone activity of Hsp60 toward urease and lay a foundation to better understand the maturation mechanism of urease in H. pylori.

Helicobacter pylori infection in children

Helicobacter pylori infection is a common problem in pediatric practice, and its acquisition is related with poor socioeconomic conditions. Although the organism is thought to be responsible for many diseases, only a handful of them have a direct causal relationship. At present, only a small number of children with well-defined clinical syndromes are benefited from testing and treatment. The treatment should include at least two antibiotics with a proton pump inhibitor.

Macromolecular assembly of Helicobacter pylori urease investigated by mass spectrometry

The supramolecular assembly of Helicobacter pylori urease was studied by nanoflow electrospray ionization orthogonal time-of-flight mass spectrometry. The measured molecular mass of the urease complex of 1.06 MDa corresponds to a dodecameric (alphabeta)(12) assembly of urease alpha (26 kDa) and beta (61 kDa) subunits. The dodecamer disassembles readily into (alphabeta)(3) subunits in solution and under controlled collisional-induced dissociation in the gas phase. This is in strong support of an ((alphabeta)(3))(4) architecture consistent with the recently published x-ray structure. In vitro, the alpha and beta subunits are capable of re-assembling to (alphabeta)(3), but not further to the dodecameric complex.

Separation and surveys of proteins of Helicobacter pylori

The analysis of Helicobacter pylori proteins is a demanding task for the elucidation of virulence factors, antigens and vaccines, all important for diagnosis, therapy and protection. In the "pre-genomic era" the purification of proteins was mostly performed by using various techniques such as detergent treatment of the bacterial cells, ultra-centrifugation, various chromatographic methods, antibody detection, N-terminal sequence determination and finally cloning and identification of the corresponding gene. In this review, the most representative methods used for purification, separation and identification of H. pylori proteins will be presented as well as some important developments in the "post-genomic era" that have improved the performance of these characterisation techniques.

The autoregulatory HspR repressor protein governs chaperone gene transcription in Helicobacter pylori

In the present study, we provide evidence that the groESL, hrcA-grpE-dnaK and cbpA-hspR-orf operons encoding the major chaperones of the human gastric pathogen Helicobacter pylori are transcribed by the vegetative sigma factor sigma80 and are regulated negatively by the transcriptional repressor HspR. In vitro studies with purified recombinant HspR protein established that the protein represses transcription by binding to large DNA regions centred around the transcription initiation site in the case of the Pcbp promoter, and around -85 and -120 in the case of the Pgro and Phrc promoters respectively. All three binding sites contain DNA motifs with some similarity to the HAIR sequence identified as a consensus for the HspR protein of Streptomyces. In contrast to the situation in Streptomyces, in which transcription of HspR-regulated genes is induced in response to heat shock, transcription of the HspR-dependent genes in H. pylori is not inducible by thermal stimuli. Transcription of the groESL and cbpA-hspR-orf operons is induced by osmotic shock, while transcription of the hrcA-grpE-dnaK operon, although HspR dependent, is not affected by salt treatment. The possibility that HspR could constitute a global transcriptional regulator for diverse cellular functions with implications for pathogenesis is discussed.

Cross-linked protein crystals for vaccine delivery

The progress toward subunit vaccines has been limited by their poor immunogenicity and limited stability. To enhance the immune response, subunit vaccines universally require improved adjuvants and delivery vehicles. In the present paper, we propose the use of cross-linked protein crystals (CLPCs) as antigens. We compare the immunogenicity of CLPCs of human serum albumin with that of soluble protein and conclude that there are marked differences in the immune response to the different forms of human serum albumin. Relative to the soluble protein, crystalline forms induce and sustain over almost a 6-month study a 6- to 10-fold increase in antibody titer for highly cross-linked crystals and an approximately 30-fold increase for lightly cross-linked crystals. We hypothesize that the depot effect, the particulate structure of CLPCs, and highly repetitive nature of protein crystals may play roles in the enhanced production of circulating antibodies. Several features of CLPCs, such as their remarkable stability, purity, biodegradability, and ease of manufacturing, make them highly attractive for vaccine formulations. This work paves the way for a systematic study of protein crystallinity and cross-linking on enhancement of humoral and T cell responses.

Extracellular release of antigenic proteins by Helicobacter pylori

Screening a Helicobacter pylori genomic library with antisera raised against H. pylori broth culture supernatant resulted in the identification of six antigens: urease, HspB, Lpp20, DnaK, MsrA, and a cysteine-rich 28-kDa protein (designated HcpA). H. pylori antigens may be released into the extracellular space by multiple mechanisms, including specific secretion pathways, autolysis, and membrane vesicle formation.

Helicobacter pylori

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma, and gastric lymphoma. H. pylori has been found in the stomachs of humans in all parts of the world. In developing countries, 70 to 90% of the population carries H. pylori. In developed countries, the prevalence of infection is lower. There appears to be no substantial reservoir of H. pylori aside from the human stomach. Transmission can occur by iatrogenic, fecal-oral, and oral-oral routes. H. pylori is able to colonize and persist in a unique biological niche within the gastric lumen. All fresh isolates of H. pylori express significant urease activity, which appears essential to the survival and pathogenesis of the bacterium. A variety of tests to diagnose H. pylori infection are now available. Histological examination of gastric tissue, culture, rapid urease testing, DNA probes, and PCR analysis, when used to test gastric tissue, all require endoscopy. In contrast, breath tests, serology, gastric juice PCR, and urinary excretion of [15N]ammonia are noninvasive tests that do not require endoscopy. In this review, we highlight advances in the detection of the presence of the organism and methods of differentiating among types of H. pylori, and we provide a background for appropriate chemotherapy of the infection.

Helicobacter pylori

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma, and gastric lymphoma. H. pylori has been found in the stomachs of humans in all parts of the world. In developing countries, 70 to 90% of the population carries H. pylori. In developed countries, the prevalence of infection is lower. There appears to be no substantial reservoir of H. pylori aside from the human stomach. Transmission can occur by iatrogenic, fecal-oral, and oral-oral routes. H. pylori is able to colonize and persist in a unique biological niche within the gastric lumen. All fresh isolates of H. pylori express significant urease activity, which appears essential to the survival and pathogenesis of the bacterium. A variety of tests to diagnose H. pylori infection are now available. Histological examination of gastric tissue, culture, rapid urease testing, DNA probes, and PCR analysis, when used to test gastric tissue, all require endoscopy. In contrast, breath tests, serology, gastric juice PCR, and urinary excretion of [15N]ammonia are noninvasive tests that do not require endoscopy. In this review, we highlight advances in the detection of the presence of the organism and methods of differentiating among types of H. pylori, and we provide a background for appropriate chemotherapy of the infection.

Acid-induced dissociation of VacA, the Helicobacter pylori vacuolating cytotoxin, reveals its pattern of assembly

In this study, we describe the ultrastructural changes associated with acid activation of Helicobacter pylori vacuolating cytotoxin (VacA). Purified VacA molecules imaged by deep-etch electron microscopy form approximately 30-nm hexagonal "flowers," each composed of an approximately 15-nm central ring surrounded by six approximately 6-nm globular "petals." Upon exposure to acidic pH, these oligomeric flowers dissociate into collections of up to 12 teardrop-shaped subunits, each measuring approximately 6 x 14 nm. Correspondingly, glycerol density gradient centrifugation shows that at neutral pH VacA sediments at approximately 22 S, whereas at acidic pH it dissociates and sediments at approximately 5 S. Immunoblot and EM analysis of the 5-S material demonstrates that it represents approximately 90-kD monomers with 6 x 14-nm "teardrop" morphology. These data indicate that the intact VacA oligomer consists of 12 approximately 90-kD subunits assembled into two interlocked six-membered arrays, overlap of which gives rise to the flower-like appearance. Support for this interpretation comes from EM identification of small numbers of relatively "flat" oligomers composed of six teardrop-shaped subunits, interpreted to be halves of the complete flower. These flat forms adsorb to mica in two different orientations, corresponding to hexameric surfaces that are either exposed or sandwiched inside the dodecamer, respectively. This view of VacA structure differs from a previous model in which the flowers were interpreted to be single layers of six monomers and the flat forms were thought to be proteolysed flowers. Since acidification has been shown to potentiate the cytotoxic effects of VacA, the present results suggest that physical disassembly of the VacA oligomer is an important feature of its activation.

Purification and characterization of urease from schizosaccharomyces pombe

The urease from the ascomycetous fission yeast Schizosaccharomyces pombe was purified about 4000-fold (34% yield) to homogeneity by acetone precipitation, ammonium sulfate precipitation, DEAE-Sepharose ion-exchange column chromatography, and if required, Mono-Q ion-exchange fast protein liquid chromatography. The enzyme was intracellular and only one species of urease was detected by nondenaturing polyacrylamide gel electrophoresis (PAGE). The native enzyme had a M(r) of 212 kDa (Sepharose CL6B-200 gel filtration) and a single subunit was detected with a M(r) of 102 kDa (PAGE with sodium dodecyl sulfate). The subunit stoichiometry was not specifically determined, but the molecular mass estimations indicate that the undissociated enzyme may be a dimer of identical subunits. The specific activity was 700-800 micromols urea.min-1.mg protein-1, the optimum pH for activity was 8.0, and the Km for urea was 1.03 mM. The sequence of the amino terminus was Met-Gln-Pro-Arg-Glu-Leu-His-Lys-Leu-Thr-Leu-His-Gln-Leu-Gly-Ser-Leu-Ala and the sequence of two tryptic peptides of the enzyme were Phe-Ile-Glu-Thr-Asn-Glu-Lys and Leu-Tyr-Ala-Pro-Glu-Asn-Ser-Pro-Gly-Phe-Val-Glu-Val-Leu-Glu-Gly-Glu-Ile- Glu- Leu-Leu-Pro-Asn-Leu-Pro. The N-terminal sequence and physical and kinetic properties indicated that S. pombe urease was more like the plant enzymes than the bacterial ureases.

The putative neuraminyllactose-binding hemagglutinin HpaA of Helicobacter pylori CCUG 17874 is a lipoprotein

The ability of certain strains of Helicobacter pylori to cause sialic acid-sensitive agglutination of erythrocytes has been attributed to the HpaA protein (D.G. Evans, T.K. Karjalainen, D. J. Evans, Jr., D. Y. Graham, and C.H. Lee, J. Bacteriol. 175:674-683, 1993), the gene for which has been cloned and sequenced. On the basis of the hydropathy plot of HpaA and the presence of a potential lipoprotein signal sequence and modification site, and because of the similarities of these features with those of the cell envelope lipoprotein Lpp20 of H. pylori, we examined the possibility that HpaA was also a lipoprotein. Posttranslational processing of the HpaA protein expressed by the cloned gene was sensitive to globomycin, an inhibitor of the lipoprotein-specific signal peptidase II. Antibodies raised to the putative sialic acid-binding region of HpaA failed to bind to the surface of H. pylori cells in immunoelectron microscopy but instead were observed to have labeled the cytoplasm when thin sections were examined. This antibody recognized a 29,000-M(r) protein in Western blots (immunoblots) of cell extracts of H. pylori and Escherichia coli cells expressing the cloned hpaA gene. Determination of the sequence of hpaA from strain CCUG 17874 indicated significant differences from that determined by Evans and coworkers in the above-mentioned study, including extension of the gene into the open reading frame 3 downstream of hpaA to produce a protein with an M(r) of 26,414. Localization of HpaA indicated that it was predominantly located in the cytoplasmic fraction of the cell in both E. coli and H. pylori. HpaA was not observed in the sarkosyl-insoluble outer membrane fraction. An isogenic mutant generated by insertional inactivation of hpaA was unaffected in its ability to bind four different human cell lines as well as fixed sections of gastric tissue and had hemagglutination properties identical to those of the wild type. The data collectively suggest that HpaA is a nonessential lipoprotein internal to the H. pylori cell and that it is not involved in adhesion.

The purification of a GroEL-like stress protein from aerobically adapted Campylobacter jejuni

From plate cultures of Campylobacter jejuni grown in room air a particulate protein of 62 kDa was isolated by ion-exchange chromatography. The protein had a square shape from the side view but when viewed from the top it had a star-shaped structure. The molecular size of the whole particle determined by gel filtration was 850 kDa which suggested the presence of 14 subunits of 62 kDa in each particle. The N-terminal 37 amino residues showed more than 80% homology with the sequence of these heat shock protein (HSP) 60 homologs of Chlamydia trachomatis, Helicobacter pylori, and Escherichia coli (GroEL). This protein is immunologically cross-reactive with the antiserum for the 60-kDa HSP of Yersinia enterocolitica. Production of the 62-kDa protein increased under heat stress and growth in an aerobic atmospheric environment. From these observations we concluded that the 62-kDa protein is a Campylobacter stress protein (Cj62) which belongs to the HSP 60 family.

Molecular biology of microbial ureases

Urease (urea amidohydrolase; EC 3.5.1.5) catalyzes the hydrolysis of urea to yield ammonia and carbamate. The latter compound spontaneously decomposes to yield another molecule of ammonia and carbonic acid. The urease phenotype is widely distributed across the bacterial kingdom, and the gene clusters encoding this enzyme have been cloned from numerous bacterial species. The complete nucleotide sequence, ranging from 5.15 to 6.45 kb, has been determined for five species including Bacillus sp. strain TB-90, Klebsiella aerogenes, Proteus mirabilis, Helicobacter pylori, and Yersinia enterocolitica. Sequences for selected genes have been determined for at least 10 other bacterial species and the jack bean enzyme. Urease synthesis can be nitrogen regulated, urea inducible, or constitutive. The crystal structure of the K. aerogenes enzyme has been determined. When combined with chemical modification studies, biophysical and spectroscopic analyses, site-directed mutagenesis results, and kinetic inhibition experiments, the structure provides important insight into the mechanism of catalysis. Synthesis of active enzyme requires incorporation of both carbon dioxide and nickel ions into the protein. Accessory genes have been shown to be required for activation of urease apoprotein, and roles for the accessory proteins in metallocenter assembly have been proposed. Urease is central to the virulence of P. mirabilis and H. pylori. Urea hydrolysis by P. mirabilis in the urinary tract leads directly to urolithiasis (stone formation) and contributes to the development of acute pyelonephritis. The urease of H. pylori is necessary for colonization of the gastric mucosa in experimental animal models of gastritis and serves as the major antigen and diagnostic marker for gastritis and peptic ulcer disease in humans. In addition, the urease of Y. enterocolitica has been implicated as an arthritogenic factor in the development of infection-induced reactive arthritis. The significant progress in our understanding of the molecular biology of microbial ureases is reviewed.

The GroES homolog of Helicobacter pylori confers protective immunity against mucosal infection in mice

Helicobacter pylori is an important etiologic agent of gastroduodenal disease. In common with other organisms, H. pylori bacteria express heat shock proteins that share homologies with the GroES-GroEL class of proteins from Escherichia coli. We have assessed the heat shock proteins of H. pylori as potential protective antigens in a murine model of gastric Helicobacter infection. Orogastric immunization of mice with recombinant H. pylori GroES- and GroEL-like proteins protected 80% (n = 20) and 70% (n = 10) of animals, respectively, from a challenge dose of 10(4) Helicobacter felis bacteria (compared to control mice, P = 0.0042 and P = 0.0904, respectively). All mice (n = 19) that were immunized with a dual antigen preparation, consisting of H. pylori GroES-like protein and the B subunit of H. pylori urease, were protected against infection. This represented a level of protection equivalent to that provided by a sonicated Helicobacter extract (P = 0.955). Antibodies directed against the recombinant H. pylori antigens were predominantly of the IgG1 class, suggesting that a type 2 T-helper cell response was involved in protection. This work reports a protein belonging to the GroES class of heat shock proteins that was shown to induce protective immunity. In conclusion, GroES-like and urease B-subunit proteins have been identified as potential components of a future H. pylori subunit vaccine.

Cell surface characteristics of Helicobacter pylori

Helicobacter pylori is an important gastroduodenal pathogen of humans. Immunological and structural studies have been performed on the phospholipids, lipopolysaccharides (LPS) and some surface proteins of H. pylori strains. H. pylori LPS has, in general, low immunological activity and this property may aid the survival of this chronic infection. Nevertheless, H. pylori LPS has been found to influence the quality of gastric mucin and to stimulate pepsinogen secretion, thereby contributing to gastric disease. A number of putative adhesins of the bacterium have been described. This multiplicity of adhesins may reflect that H. pylori adherence is a multi-step process involving different interactions, and that different adhesins may mediate adherence to various sites in gastric tissue.

Helicobacter pylori hspA-hspB heat-shock gene cluster: nucleotide sequence, expression, putative function and immunogenicity

All Helicobacter pylori isolates synthesize a 54 kDa immunodominant protein that was reported to be associated with the nickel-dependent urease of H. pylori. This protein was recently recognized as a homologue of the heat-shock protein of the GroEL class. The gene encoding the GroEL-like protein of H. pylori (HspB) was cloned (pILL689) and was shown to belong to a bicistronic operon including the hspA and hspB genes. In Escherichia coli, the constitutive expression of the hspA and hspB genes was initiated from a promoter located within an IS5 insertion element that mapped upstream to the two open reading frames (ORFs). IS5 was absent from the H. pylori genome, and was thus acquired during the cosmid cloning process. hspA and hspB encoded polypeptides of 118 and 545 amino acid residues, corresponding to calculated molecular masses of 13.0 and 58.2 kDa, respectively. Amino acid sequence comparison studies revealed that, although H. pylori HspA and HspB proteins were highly similar to their bacterial homologues, the H. pylori HspA featured a striking motif at the C-terminus. This unique motif consists of a series of cysteine and histidine residues resembling a nickel-binding domain, which is not present in any of the other bacterial GroES homologues so far characterized. When the pILL689 recombinant plasmid was introduced together with the H. pylori urease gene cluster (pILL763) into an E. coli host strain, an increase of urease activity was observed. This suggested a close interaction between the HspA and HspB proteins and the urease enzyme, and a possible role for HspA in the chelation of nickel ions. The genes encoding each of the HspA and HspB polypeptides were cloned, expressed independently as proteins fused to the maltose-binding protein (MBP) and purified in large scale. The MBP-HspA and MBP-HspB fusion proteins were shown to retain their antigenic properties. Both HspA and HspB represent antigens that are specifically recognized by the sera from H. pylori-infected patients. Whereas HspB was known to be immunogenic in humans, this is the first demonstration that HspA per se is also immunogenic.

Non-motile mutants of Helicobacter pylori and Helicobacter mustelae defective in flagellar hook production

Flagellar hooks were purified from Helicobacter pylori and Helicobacter mustelae. The 70 x 16 nm H. pylori hook was composed of FlgE subunits of 78kDa, while the 72 x 16 nm H. mustelae hook was composed of 87 kDa subunits. N-terminal sequence was obtained for the FlgE proteins of both species, and for an internal H. mustelae FlgE peptide. Degenerate oligonucleotide primers allowed amplification of a 1.2 kb fragment from the H. mustelae chromosome, which carried part of the flgE gene. The corresponding H. pylori gene was cloned by immunoscreening of a genomic library constructed in lambda ZAP Express. The translated H. pylori flgE sequence indicated a protein with limited homology with the hook proteins from Salmonella typhimurium and Treponema phagedenis. Mutants of H. pylori and H. mustelae defective in hook production generated by allele replacement were non-motile and devoid of flagellar filaments but produced both flagellin subunits, which were localized in the soluble fraction of the cell. The level of flagellin production was unchanged in the mutants, indicating that the regulation of flagellin expression in Helicobacter differs from that in the Enterobacteriaceae.

Identification of surface-exposed outer membrane antigens of Helicobacter pylori

Despite the potential significance of surface-localized antigens in the colonization by and disease processes of Helicobacter pylori, few such components have been unequivocally identified and/or characterized. To further investigate the surface of this bacterium, monoclonal antibodies (MAbs) to a sarcosine-insoluble outer membrane fraction prepared from H. pylori NCTC 11637 were raised. MAbs were selected on the basis of their surface reactivity to whole cells by enzyme-linked immunosorbent assay, immunofluorescence, and immunoelectron microscopy. By use of this selection protocol, 14 surface-reactive MAbs were chosen. These MAbs were used to identify six protein antigens (molecular masses, 80, 60, 51, 50, 48, and 31 kDa), all of which were localized within or associated with the outer membrane. Two of the MAbs recognized the core region of lipopolysaccharide (LPS). Only these two anti-LPS MAbs also recognized the flagellar sheath, indicating a structural difference between the sheath and outer membrane. Three of the protein antigens (80, 60, and 51 kDa) were strain specific, while the other three antigens were present in other strains of H. pylori. Both the 51- and 48-kDa antigens were heat modifiable and likely are porins. A conserved 31-kDa protein may represent another species of porin. A method involving sucrose density ultracentrifugation and Triton extraction that allows the preparation of H. pylori outer membranes with minimal inner membrane contamination is described. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that the protein content of the H. pylori outer membrane is similar structurally to those of other species of Helicobacter but markedly different from those of taxonomically related Campylobacter spp. and Escherichia coli. H. pylori also appeared to lack peptidoglycan-associated proteins.

Molecular characterization of a conserved 20-kilodalton membrane-associated lipoprotein antigen of Helicobacter pylori

Antisera raised in rabbits to whole cells of Helicobacter pylori recognized as a major antigen a protein with an apparent molecular weight of 20,000. The antigen was purified by differential solubilization with N-octyl-beta-D-glucopyranoside, urea, and sodium dodecyl sulfate followed by molecular sieving. The mass of the protein, Lpp20, was 18,283 Da as determined by mass spectrometry. The lpp20 gene encoding this protein was cloned in Escherichia coli by using the vector lambda EMBL3, and plasmid subclones expressed the full-length protein from the native H. pylori promoter. lpp20 was mapped to the same 358-kb NruI fragment as flaB. DNA sequence analysis showed that the gene was 525 bp long and encoded a 175-amino-acid protein with a molecular weight of 19,094 containing a 21-residue typical lipoprotein signal peptide and consensus prolipoprotein processing site. The mass of the deduced 154-residue mature protein was 16,865 Da. Growth of E. coli cells expressing the cloned H. pylori lpp20 gene in the presence of [3H]palmitic acid resulted in radiolabelled Lpp20 while treatment of the E. coli cells with globomycin caused accumulation of unprocessed Lpp20, consistent with Lpp20 being a lipoprotein. Lpp20 cofractionated with the cytoplasmic membrane fraction, although a proportion of the protein was also found in the outer membrane. A mutant generated by mutant-allele exchange displayed normal viability, showing that Lpp20 belonged to the nonessential class of lipoproteins.

Urease from Staphylococcus saprophyticus: purification, characterization and comparison to Staphylococcus xylosus urease

Urease from Staphylococcus saprophyticus was purified more than 800-fold by liquid chromatography reaching homogeneity, as shown by isoelectric focussing, at a maximum specific activity of 1979 U/mg. The molecular weight of the native enzyme was 420,000; it consisted of subunits with molecular weights of 72,400 (alpha), 20,400 (beta), 13,900 (gamma) in an estimated (alpha beta gamma)4 stoichiometry. In native gradient polyacrylamide gel electrophoresis urease exhibited a multiple activity band pattern with molecular weights ranging from 420,000 to 100,000. In the native enzyme, 4.09 (+/- 0.25) atoms of nickel per molecule were detected. The N-terminal amino acids of the urease subunits were identical to those from Staphylococcus xylosus, and amino acid analysis revealed high similarities in both enzymes; no cysteine was detected after acid hydrolysis of vinylpyridinylated urease. Electron micrographs of negatively stained urease specimens from both staphylococci showed identical size and structure.

Identification and molecular characterization of a major ring-forming surface protein from the gastric pathogen Helicobacter mustelae

The spiral microaerophilic bacterium Helicobacter mustelae is linked to gastritis and gastric ulcers in ferrets. Electron microscopy of H. mustelae showed the presence of a laterally extensive array of 8.5-nm-diameter rings on the cell surface, which was shown to be composed of a 150kDa protein. This protein was purified, and the sequence of 10 amino-terminal residues was determined. Polyclonal antibody against the purified 150 kDa protein labelled the ring structures on the homologous strain by means of immunogold. Cross-reactive proteins were identified in three H. mustelae strains, but not in Helicobacter pylori or Helicobacter felis. The hsr gene encoding this protein was cloned, and the protein expressed in Escherichia coli independently of vector promoters. The 1519-codon nucleotide sequence of the gene was determined, and comparison with the chemically derived protein sequence indicated a 47-residue leader peptide, and a mature protein with a molecular weight of 152,300. Thus the cell surface of H. mustelae differs markedly from other members of the genus Helicobacter in being covered by an array of 8.5 nm rings composed of a 150kDa protein.

The Hsp60 protein of Helicobacter pylori: structure and immune response in patients with gastroduodenal diseases

Helicobacter pylori is a human pathogen that has been associated with gastritis, peptic ulcer and gastric carcinoma. The role of the direct action of H. pylori virulence factors and of the induction of autoreactive immunity in the development of chronic gastritis has not been clarified yet. Here we report the cloning and molecular characterization of a gene of H. pylori coding for a protein of 58 kDa, recognized by sera of patients affected by H. pylori-induced gastroduodenal diseases. This antigen is present in all the H. pylori strains tested and it belongs to the Hsp60 family of heat-shock proteins, with high homology with other bacterial and eukaryotic proteins of the same family. This class of homologous proteins has been implicated in the induction of autoimmune disorders in different systems. The presence in infected patients of anti-H. pylori Hsp60 antibodies, potentially cross-reactivity between human Hsp60 and a rabbit antiserum against H. pylori Hsp60 suggest that a role of this protein in gastroduodenal diseases is possible.