Structural basis and functional consequence of Helicobacter pylori CagA multimerization in cells

Helicobacter pylori cagA-positive strains are associated with gastric adenocarcinoma. The cagA gene product CagA is delivered into gastric epithelial cells where it localizes to the plasma membrane and undergoes tyrosine phosphorylation at the EPIYA-repeat region, which contains the EPIYA-A segment, EPIYA-B segment, and Western CagA-specific EPIYA-C or East Asian CagA-specific EPIYA-D segment. In host cells, CagA specifically binds to and deregulates SHP-2 phosphatase via the tyrosine-phosphorylated EPIYA-C or EPIYA-D segment, thereby inducing an elongated cell shape known as the hummingbird phenotype. In this study, we found that CagA multimerizes in cells in a manner independent of its tyrosine phosphorylation. Using a series of CagA mutants, we identified a conserved amino acid sequence motif (FPLXRXXXVXDLSKVG), which mediates CagA multimerization, within the EPIYA-C segment as well as in a sequence that located immediately downstream of the EPIYA-C or EPIYA-D segment. We also found that a phosphorylation-resistant CagA, which multimerizes but cannot bind SHP-2, inhibits the wild-type CagA-SHP-2 complex formation and abolishes induction of the hummingbird phenotype. Thus, SHP-2 binds to a preformed and tyrosinephosphorylated CagA multimer via its two Src homology 2 domains. These results, in turn, indicate that CagA multimerization is a prerequisite for CagA-SHP-2 interaction and subsequent deregulation of SHP-2. The present work raises the possibility that inhibition of CagA multimerization abolishes pathophysiological activities of CagA that promote gastric carcinogenesis.     

Structural characterization of the lipid A component of Helicobacter pylori rough- and smooth-form lipopolysaccharides.

The chemical structure of free lipid A isolated from rough- and smooth-form lipopolysaccharides (R-LPS and S-LPS, respectively) of the human gastroduodenal pathogen Helicobacter pylori was elucidated by compositional and degradative analysis, nuclear magnetic resonance spectroscopy, and mass spectrometry. The predominant molecular species in both lipid A components are identical and tetraacylated, but a second molecular species which is hexaacylated is also present in lipid A from S-LPS. Despite differences in substitution by acyl chains, the hydrophilic backbone of the molecules consisted of beta(1,6)-linked D-glucosamine (GlcN) disaccharide 1-phosphate. Because of microheterogeneity, nonstoichiometric amounts of ethanolamine-phosphate were also linked to the glycosidic hydroxyl group. In S-LPS, but not in R-LPS, the hydroxyl group at position 4' was partially substituted by another phosphate group. Considerable variation in the distribution of fatty acids on the lipid A backbone was revealed by laser desorption mass spectrometry. In tetraacyl lipid A, the amino group of the reducing GlcN carried (R)-3-hydroxyoctadecanoic acid (position 2), that of the nonreducing GlcN carried (R)-3-(octadecanoyloxy)octadecanoic acid (position 2'), and ester-bound (R)-3-hydroxyhexadecanoic acid was attached at position 3. Hexaacyl lipid A had a similar substitution by fatty acids, but in addition, ester-bound (R)-3-(dodecanoyloxy)hexadecanoic acid or (R)-3(tetradecanoyloxy)hexadecanoic acid was attached at position 3'. The predominant absence of ester-bound 4'-phosphate and the presence of tetraacyl lipid A with fatty acids of 16 to 18 carbons in length differentiate H. pylori lipid A from that of other bacterial species and help explain the low endotoxic and biological activities of H. pylori LPS.     

Purification and characterization of urease from Helicobacter pylori

Urease was purified 112-fold to homogeneity from the microaerophilic human gastric bacterium, Helicobacter pylori. The urease isolation procedure included a water extraction step, size exclusion chromatography, and anion exchange chromatography. The purified enzyme exhibited a Km of 0.3 +/- 0.1 mM and a Vmax of 1,100 +/- 200 mumols of urea hydrolyzed/min/mg of protein at 22 degrees C in 31 mM Tris-HCl, pH 8.0. The isoelectric point was 5.99 +/- 0.03. Molecular mass estimated for the native enzyme was 380,000 +/- 30,000 daltons, whereas subunit values of 62,000 +/- 2,000 and 30,000 +/- 1,000 were determined. The partial amino-terminal sequence (17 residues) of the large subunit of H. pylori urease (Mr = 62,000) was 76% homologous with an internal sequence of the homohexameric jack bean urease subunit (Mr = 90,770; Takashima, K., Suga, T., and Mamiya, G. (1988) Eur. J. Biochem. 175, 151-165) and was 65% homologous with amino-terminal sequences of the large subunits of heteropolymeric ureases from Proteus mirabilis (Mr = 73,000) and from Klebsiella aerogenes (Mr = 72,000; Mobley, H. L. T., and Hausinger, R. P. (1989) Microbiol. Rev. 53, 85-108). The amino-terminal sequence (20 residues) of the small subunit of H. pylori urease (Mr = 30,000) was 65 and 60% homologous with the amino-terminal sequences of the subunit of jack bean urease and with the Mr = 11,000 subunit of P. mirabilis urease (Jones, B. D., and Mobley, H. L. T. (1989) J. Bacteriol. 171, 6414-6422), respectively. Thus, the urease of H. pylori shows similarities to ureases found in plants and other bacteria. When used as antigens in an enzyme-linked immunosorbent assay, neither purified urease nor an Mr = 54,000 protein that co-purified with urease by size exclusion chromatography was as effective as crude preparations of H. pylori proteins at distinguishing sera from persons known either to be infected with H. pylori or not.     

Functional characterization of Helicobacter pylori DnaB helicase

Helicobacter pylori causes gastric ulcer diseases and gastric adenocarcinoma in humans. Not much is known regarding DNA replication in H.pylori that is important for cell survival. Here we report the cloning, expression and characterization of H.pylori DnaB (HpDnaB) helicase both in vitro and in vivo. Among the DnaB homologs, only Escherichia coli DnaB has been studied extensively. HpDnaB showed strong 5′ to 3′ helicase and ATPase activity. Interestingly, H.pylori does not have an obvious DnaC homolog which is essential for DnaB loading on the E.coli chromosomal DNA replication origin (oriC). However, HpDnaB can functionally complement the E.coli DnaB temperature-sensitive mutant at the non-permissive temperature, confirming that HpDnaB is a true replicative helicase. Escherichia coli DnaC co-eluted in the same fraction with HpDnaB following gel filtration analysis suggesting that these proteins might physically interact with each other. It is possible that a functional DnaC homolog is present in H.pylori. The complete characterization of H.pylori DnaB helicase will also help the comparative analysis of DnaB helicases among bacteria.     

Genotypic characterization of clarithromycin-resistant Helicobacter pylori strains

Helicobacterpylori (Hp) resistance to clarithromycin, one of the antibiotics most used to eradicate infection, is connected with the presence of a point mutation on the level of adenine at position 2143 or 2144 of 23S rRNA. AIM: The aim of the study is to evaluate of the presence of these mutation vs control clarithromycin resistant Hp strains present in North Sardinia; to verify the real association between the type of mutation and the resistance-level; to use easier molecular biology methods to quickly locate the resistance-associated mutations beginning with the bioptic material. The clarithromycin susceptibility of Hp isolates was tested by the E-test method (antibiotic assay). Genomic DNA of Hp strains was amplified using specific primers for the domain V. of ribosomic 23S rRNA and sequenced after the reaction with a primer within the fragment 23S. At the same time PCR-RFLP reliability was examined underlining the presence of these mutations with BsaI, BbsI, MboII restriction enzymes. Two mutations in 2143 (A- - G) and 2144 (A- - G) were found by domain V sequencing. The strains with mutation 2143 are characterized by a greater resistance level (MIC>64 g/ml) than those with mutation 2144 (MIC <64 g/ml). Restriction endonucleases BbsI and MboII recognise the site containing the mutation 2143 (A- - G), while BsaI recognise the mutation 2144 (A- - G). These methods might enable us to identify the presence of Hp directly from bioptic material and possible clarithromycin resistance and plan a suitable therapeutic strategy and consequently a better control of the infection.     

Purification and characterization of neutral sphingomyelinase from Helicobacter pylori

Phospholipase activities of human gastric bacterium, Helicobacter pylori, are regarded as the pathogenic factors owing to their actions on epithelial cell membranes. In this study, we purified and characterized neutral sphingomyelinase (N-SMase) from the superficial components of H. pylori strains for the first time. N-SMase was purified 2083-fold with an overall recovery of 37%. The purification steps included acid glycine extraction, ammonium sulfate precipitation, CM-Sepharose, Mono-Q, and Sephadex G-75 column chromatography. Approximate molecular mass for the native N-SMase was around 32 kDa. When N-omega-trinitrophenylaminolauryl sphingomyelin (TNPAL-SM) was used as a substrate, the purified enzyme exhibited a K(m) of 6.7 microM and a V(max) of 15.6 nmol of TNPAL-sphingosine/h/mg of protein at 37 degrees C in 50 mM phosphate-buffered saline, pH 7.4. N-SMase reaches optimal activity at pH 7.4 and has a pI of 7.15. The enzyme activity is magnesium dependent and specifically hydrolyzed sphingomyelin and phosphatidylethanolamine. The enzyme also exhibits hemolytic activity on human erythrocytes. According to Western blot analysis, a rabbit antiserum against purified N-SMase from H. pylori cross-reacted with SMase from Bacillus cereus. Sera from individuals with H. pylori infection but not uninfected ones recognizing the purified N-SMase indicated that it was produced in vivo. In enzyme-linked immunosorbent assays, the purified N-SMase used as an antigen was as effective as crude protein antigens in detecting human antibodies to H. pylori.     

Structural and functional characterization of PseC, an aminotransferase involved in the biosynthesis of pseudaminic acid, an essential flagellar modification in Helicobacter pylori

Helicobacter pylori flagellin is heavily glycosylated with the novel sialic acid-like nonulosonate, pseudaminic acid (Pse). The glycosylation process is essential for assembly of functional flagellar filaments and consequent bacterial motility. Because motility is a key virulence factor for this and other important pathogens, the Pse biosynthetic pathway offers potential for novel therapeutic targets. From recent NMR analyses, we determined that the conversion of UDP-alpha-D-Glc-NAc to the central intermediate in the pathway, UDP-4-amino-4,6-dideoxy-beta-L-AltNAc, proceeds by formation of UDP-2-acetamido-2,6-dideoxy-beta-L-arabino-4-hexulose by the dehydratase/epimerase PseB (HP0840) followed with amino transfer by the aminotransferase, PseC (HP0366). The central role of PseC in the H. pylori Pse biosynthetic pathway prompted us to determine crystal structures of the native protein, its complexes with pyridoxal phosphate alone and in combination with the UDP-4-amino-4,6-dideoxy-beta-L-AltNAc product, the latter being converted to the external aldimine form in the active site of the enzyme. In the binding site, the AltNAc sugar ring adopts a 4C1 chair conformation, which is different from the predominant 1C4 form found in solution. The enzyme forms a homodimer where each monomer contributes to the active site, and these structures have permitted the identification of key residues involved in stabilization, and possibly catalysis, of the beta-L-arabino intermediate during the amino transfer reaction. The essential role of Lys183 in the catalytic event was confirmed by site-directed mutagenesis. This work presents for the first time a nucleotide-sugar aminotransferase co-crystallized with its natural ligand, and, in conjunction with the recent functional characterization of this enzyme, these results will assist in elucidating the aminotransferase reaction mechanism within the Pse biosynthetic pathway.     

Helicobacter pylori CagA tertiary structure reveals functional insights

CagA is a major disease-associated factor injected by the gastric pathogen Helicobacter pylori. In this issue, Hayashi et al. (2012) report the crystallographic structure of the CagA N terminus (residues 24-876) at 3.19 ? resolution. This study revealed three distinct domains, giving novel insights into intramolecular and intermolecular protein and phosphatidylserine interactions.     

Purification and characterization of cytochrome c-553 from Helicobacter pylori

Helicobacter pylori, a microaerophilic Gram-negative spiral bacterium residing in the human stomach, contains a small size soluble cytochrome c. This cytochrome c was purified from the soluble fraction of H. pylori by conventional chromatographies involving octyl-cellulose and CM-Toyopearl. Its reduced form gave an alpha absorption band at 553 nm, and thus the cytochrome was named H. pylori cytochrome c-553. The cytochrome, giving a band below 10,000 Da upon SDS-PAGE, was determined to have a mass of 8,998 by time of flight mass spectroscopy. Its N-terminal peptide sequence was TDVKALAKS---, indicating that the nascent polypeptide was cleaved to produce a signal peptide of 19 amino acid residues and a mature protein composed of 77 amino acid residues. The cb-type cytochrome c oxidase oxidized ferrocytochrome c-553 of this bacterium actively (V(max) of about 250 s(-1)) with a small K(m) (0.9 microM). Analysis of the effect of the salt concentration on the oxidase activity indicated that oxidation of cytochrome c-553 is highly inhibited under high ionic conditions. The amino acid sequence of H. pylori cytochrome c-553 showed the closest similarity to that of Desulfovibrio vulgaris cytochrome c-553, and these sequences showed a weak relationship to that of the cytochrome c(8)-group among class I cytochromes c.     

Identification and characterization of an aliphatic amidase in Helicobacter pylori

We report, for the first time, the presence in Helicobacter pylori of an aliphatic amidase that, like urease, contributes to ammonia production. Aliphatic amidases are cytoplasmic acylamide amidohydrolases (EC 3.5.1.4) hydrolysing short-chain aliphatic amides to produce ammonia and the corresponding organic acid. The finding of an aliphatic amidase in H. pylori was unexpected as this enzyme has only previously been described in bacteria of environmental (soil or water) origin. The H. pylori amidase gene amiE (1017 bp) was sequenced, and the deduced amino acid sequence of AmiE (37 746 Da) is very similar (75% identity) to the other two sequenced aliphatic amidases, one from Pseudomonas aeruginosa and one from Rhodococcus sp. R312. Amidase activity was measured as the release of ammonia by sonicated crude extracts from H. pylori strains and from recombinant Escherichia coli strains overproducing the H. pylori amidase. The substrate specificity was analysed with crude extracts from H. pylori cells grown in vitro; the best substrates were propionamide, acrylamide and acetamide. Polymerase chain reaction (PCR) amplification of an internal amiE sequence was obtained with each of 45 different H. pylori clinical isolates, suggesting that amidase is common to all H. pylori strains. A H. pylori mutant (N6-836) carrying an interrupted amiE gene was constructed by allelic exchange. No amidase activity could be detected in N6-836. In a N6–urease negative mutant, amidase activity was two- to threefold higher than in the parental strain N6. Crude extracts of strain N6 slowly hydrolysed formamide. This activity was affected in neither the amidase negative strain (N6-836) nor a double mutant strain deficient in both amidase and urease activities, suggesting the presence of an independent discrete formamidase in H. pylori. The existence of an aliphatic amidase, a correlation between the urease and amidase activities and the possible presence of a formamidase indicates that H. pylori has a large range of possibilities for intracellular ammonia production.     

Purification and characterization of protein methylase II from Helicobacter pylori

Protein methylase II (AdoMet:protein-carboxyl O-methyltransferase, EC 2.1.1.24) was identified and purified 115-fold from Helicobacter pylori through Q-Sepharose ion exchange column, AdoHcy-Sepharose 4B column, and Superdex 200 HR column chromatography using FPLC. The purified preparation showed two protein bands of about 78 kDa and 29 kDa molecular mass on SDS-PAGE. On non-denaturing gel electrophoresis, the enzyme migrated as a single band with a molecular mass of 410 kDa. In addition, MALDI-TOF-MS analysis and Superdex 200 HR column chromatography of the purified enzyme showed a major mass signal with molecular mass values of 425 kDa and 430 kDa, respectively. Therefore, the above results led us to suggest that protein methylase II purified from H. pylori is composed of four heterodimers with 425 kDa (4x(78+29)=428 kDa). This magnitude of molecular mass is unusual for protein methylases II so far reported. The enzyme has an optimal pH of 6.0, a K(m) value of 5.0x10(-6) M for S-adenosyl-L-methionine and a V(max) of 205 pmol methyl-(14)C transferred min(-1) mg(-1) protein.     

Structural and biochemical characterization of HP0315 from Helicobacter pylori as a VapD protein with an endoribonuclease activity

VapD-like virulence-associated proteins have been found in many organisms, but little is known about this protein family including the 3D structure of these proteins. Recently, a relationship between the Cas2 family of ribonucleases associated with the CRISPR system of microbial immunity and VapD was suggested. Here, we show for the first time the structure of a member of the VapD family and present a relationship of VapD with Cas2 family and toxin–antitoxin (TA) systems. The crystal structure of HP0315 from Helicobacter pylori was solved at a resolution of 2.8 Å. The structure of HP0315, which has a modified ferredoxin-like fold, is very similar to that of the Cas2 family. Like Cas2 proteins, HP0315 shows endoribonuclease activity. HP0315-cleaved mRNA, mainly before A and G nucleotides preferentially, which means that HP0315 has purine-specific endoribonuclease activity. Mutagenesis studies of HP0315 revealed that D7, L13, S43 and D76 residues are important for RNase activity, in contrast, to the Cas2 family. HP0315 is arranged as an operon with HP0316, which was found to be an antitoxin-related protein. However, HP0315 is not a component of the TA system. Thus, HP0315 may be an evolutionary intermediate which does not belong to either the Cas2 family or TA system.     

Structural basis for shikimate-binding specificity of Helicobacter pylori shikimate kinase

Shikimate kinase (EC 2.7.1.71) catalyzes the specific phosphorylation of the 3-hydroxyl group of shikimic acid in the presence of ATP. As the fifth key step in the shikimate pathway for aromatic amino acid biosynthesis in bacteria, fungi, and plants, but not mammals, shikimate kinase represents an attractive target for the development of new antimicrobial agents, herbicides, and antiparasitic agents. Here, we report the 1.8-Angstroms crystal structure of Helicobacter pylori shikimate kinase (HpSK). The crystal structure shows a three-layer alpha/beta fold consisting of a central sheet of five parallel beta-strands flanked by seven alpha-helices. An HpSK-shikimate-PO(4) complex was also determined and refined to 2.3 Angstroms, revealing induced-fit movement from an open to a closed form on substrate binding. Shikimate is located above a short 3(10) helix formed by a strictly conserved motif (GGGXV) after beta(3). Moreover, several highly conserved charged residues including Asp33 (in a conserved DT/SD motif), Arg57, and Arg132 (interacting with shikimate) are identified, guiding the development of novel inhibitors of shikimate kinase.     

Structural and functional characterization of calponin fragments

Calponin from chicken gizzard consists of two principal components, possibly isoforms, separable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing. Cleavage with 2-nitro-5-thiocyanobenzoic acid indicated that calponin contains 2 cysteine residues. Purified fragments of 30 and 21 kDa retained the following properties of the intact protein: actin-, tropomyosin- and calmodulin-binding, and ability to inhibit the actin-activated MgATPase activity of smooth muscle myosin. Both fragments, like intact calponin, were phosphorylated by protein kinase C which inhibited their binding to actin and relieved their inhibition of the ATPase. Tryptic digestion of calponin phosphorylated by protein kinase C generated 3 phosphopeptides with the following N-terminal sequences: FASQQGMTAYGTR, GASQQGMTVYGLP, and NHSGHVQ, each possessing a single phosphoserine.     

Functional characterization of UvrD helicases from Haemophilus influenzae and Helicobacter pylori

Haemophilus influenzae and Helicobacter pylori are major bacterial pathogens that face high levels of genotoxic stress within their host. UvrD, a ubiquitous bacterial helicase that plays important roles in multiple DNA metabolic pathways, is essential for genome stability and might, therefore, be crucial in bacterial physiology and pathogenesis. In this study, the functional characterization of UvrD helicase from Haemophilus influenzae and Helicobacter pylori is reported. UvrD from Haemophilus influenzae (HiUvrD) and Helicobacter pylori (HpUvrD) exhibit strong single-stranded DNA-specific ATPase and 3'-5' helicase activities. Mutation of highly conserved arginine (R288) in HiUvrD and glutamate (E206) in HpUvrD abrogated their activities. Both the proteins were able to bind and unwind a variety of DNA structures including duplexes with strand discontinuities and branches, three- and four-way junctions that underpin their role in DNA replication, repair and recombination. HiUvrD required a minimum of 12 nucleotides, whereas HpUvrD preferred 20 or more nucleotides of 3'-single-stranded DNA tail for efficient unwinding of duplex DNA. Interestingly, HpUvrD was able to hydrolyze and utilize GTP for its helicase activity although not as effectively as ATP, which has not been reported to date for UvrD characterized from other organisms. HiUvrD and HpUvrD were found to exist predominantly as monomers in solution together with multimeric forms. Noticeably, deletion of distal C-terminal 48 amino acid residues disrupted the oligomerization of HiUvrD, whereas deletion of 63 amino acids from C-terminus of HpUvrD had no effect on its oligomerization. This study presents the characteristic features and comparative analysis of Haemophilus influenzae and Helicobacter pylori UvrD, and constitutes the basis for understanding the role of UvrD in the biology and virulence of these pathogens.     

Purification and characterization of the vacuolating toxin from Helicobacter pylori.

A vacuolating toxin was purified to homogeneity from broth culture supernatant of the human gastric bacterium, Helicobacter pylori. The procedure for isolating the toxin included ammonium sulfate precipitation, hydrophobic interactive chromatography, size exclusion chromatography, and anion exchange chromatography, which together resulted in a greater than 5000-fold purification of toxin activity. The molecular mass of the purified, denatured toxin was 87,000 +/- 320 daltons, and the native toxin was an aggregate with a molecular mass greater than or equal to 972,000 daltons. The amino-terminal sequence of the purified toxin was partially homologous with internal sequences of numerous transport or ion channel proteins. Antiserum raised against the M(r) = 87,000 protein neutralized toxin activity, whereas preimmune serum did not. When reacted with specific antiserum to the M(r) = 87,000 protein in an enzyme-linked immunosorbent (ELISA) assay, culture supernatants from eight tox+ H. pylori strains produced significantly higher optical density readings than eight tox- supernatants (0.614 +/- 0.11 versus 0.046 +/- 0.01, p less than 0.0001). Sera from H. pylori-infected humans recognized the purified M(r) = 87,000 protein significantly better by ELISA than sera from uninfected persons (0.424 +/- 0.06 versus 0.182 +/- 0.02, p = 0.0009). Finally, ELISA recognition of the purified M(r) = 87,000 protein by human sera was significantly associated with toxin-neutralizing activity (p = 0.019, r = 0.518).     

Biochemical characterization and inhibitor discovery of shikimate dehydrogenase from Helicobacter pylori

Shikimate dehydrogenase (SDH) is the fourth enzyme involved in the shikimate pathway. It catalyzes the NADPH-dependent reduction of 3-dehydroshikimate to shikimate, and has been developed as a promising target for the discovery of antimicrobial agent. In this report, we identified a new aroE gene encoding SDH from Helicobacter pylori strain SS1. The recombinant H. pylori shikimate dehydrogenase (HpSDH) was cloned, expressed, and purified in Escherichia coli system. The enzymatic characterization of HpSDH demonstrates its activity with k(cat) of 7.7 s(-1) and K(m) of 0.148 mm toward shikimate, k(cat) of 7.1 s(-1) and K(m) of 0.182 mm toward NADP, k(cat) of 5.2 s(-1) and K(m) of 2.9 mm toward NAD. The optimum pH of the enzyme activity is between 8.0 and 9.0, and the optimum temperature is around 60 degrees C. Using high throughput screening against our laboratory chemical library, five compounds, curcumin (1), 3-(2-naphthyloxy)-4-oxo-2-(trifluoromethyl)-4H-chromen-7-yl 3-chlorobenzoate (2), butyl 2-{[3-(2-naphthyloxy)-4-oxo-2-(trifluoromethyl)-4H-chromen-7-yl]oxy}propanoate (3), 2-({2-[(2-{[2-(2,3-dimethylanilino)-2-oxoethyl]sulfanyl}-1,3-benzothiazol-6-yl)amino]-2-oxoethyl}sulfanyl)-N-(2-naphthyl)acetamide (4), and maesaquinone diacetate (5) were discovered as HpSDH inhibitors with IC(50) values of 15.4, 3.9, 13.4, 2.9, and 3.5 microm, respectively. Further investigation indicates that compounds 1, 2, 3, and 5 demonstrate noncompetitive inhibition pattern, and compound 4 displays competitive inhibition pattern with respect to shikimate. Compounds 1, 4, and 5 display noncompetitive inhibition mode, and compounds 2 and 3 show competitive inhibition mode with respect to NADP. Antibacterial assays demonstrate that compounds 1, 2, and 5 can inhibit the growth of H. pylori with MIC of 16, 16, and 32 microg.mL(-1), respectively. This current work is expected to favor better understanding the features of SDH and provide useful information for the development of novel antibiotics to treat H. pylori-associated infection.     

Structural comparison of urease and a GroEL analog from Helicobacter pylori.

Electron microscopy of purified protein preparations indicated that Helicobacter pylori urease consisted of circular particles that are 13 nm in diameter, some of which showed indications of threefold rotational symmetry. A GroEL analog of H. pylori (Hp60K) appeared as a disc-shaped molecule with a diameter similar to that of urease but possessed sevenfold rotational symmetry. In a side-view projection, Hp60K appeared as two or four discs stacked side by side.