Gender trends in dentistry: Dental faculty and academic leadership

OBJECTIVES

Gender equality in the healthcare workforce has been a topic of discourse for many decades. In dental academia, women's representation of enrolled students and faculty has risen consistently since the 1980s. However, women in faculty leadership positions may still be lagging when compared to men. The purpose of this study was to evaluate the number of women who occupy the upper echelons of academic rank and title by analyzing cross-referenced data from the American Dental Association and the American Dental Education Association on women dental school graduates in relation to academic appointments.

METHODS

Gender distribution in rank, title, and appointments in the decade from 2011 to 2019, as well as percentage of women graduates over the same period, were collected for descriptive statistics. Multiple linear regression analysis, Cochran Armitage, and chi-square tests were conducted to examine trends over the years and to determine significant differences in overall percentages (p < 0.05).

RESULTS

The total women faculty percentages ranged from 36% to 40%. While the lower-level rank of instructor retained a higher representation of women (56%-65%), the higher rank of professor had disproportionately lower women percentages (18%-26%). Graduates, full-time faculty, lower-level academic ranks, and higher-level academic ranks for women followed similar upward trends that were statistically significant (p < 0.05). When comparing the different groups against each other, the annual increase in women DMD/DDS graduate percentage was higher than women full-time faculty (0.28%), instructor rank (0.92%), professor rank (0.50%), and department chair appointments (0.49%).

CONCLUSIONS

Our data show that women are still underrepresented at higher academic ranks. However, the upward trends for professors, assistant deans, and program chairs suggest that in recent years, more women faculty may have been encouraged, mentored, or offered higher administrative positions in academic institutions.

Inactive USP14 and inactive UCHL5 cause accumulation of distinct ubiquitinated proteins in mammalian cells

USP14 is a cysteine protease deubiquitinase associated with the proteasome and plays important catalytic and allosteric roles in proteasomal degradation. USP14 inhibition has been considered a therapeutic strategy for accelerating degradation of aggregation-prone proteins in neurodegenerative diseases and for inhibiting proteasome function to induce apoptotic cell death in cancers. Here we studied the effects of USP14 inhibition in mammalian cells using small molecule inhibitors and an inactive USP14 mutant C114A. Neither the inhibitors nor USP14 C114A showed consistent or significant effects on the level of TDP-43, tau or α-synuclein in HEK293T cells. However, USP14 C114A led to a robust accumulation of ubiquitinated proteins, which were isolated by ubiquitin immunoprecipitation and identified by mass spectrometry. Among these proteins we confirmed that ubiquitinated β-catenin accumulated in the cells expressing USP14 C114A with immunoblotting and immunoprecipitation experiments. The proteasome binding domain of USP14 C114A is required for its effect on ubiquitinated proteins. UCHL5 is the other cysteine protease deubiquitinase associated with the proteasome. Interestingly, the inactive mutant of UCHL5 C88A also caused an accumulation of ubiquitinated proteins in HEK293T cells but did not affect β-catenin, demonstrating USP14 but not UCHL5 has a specific effect on β-catenin. We used ubiquitin immunoprecipitation and mass spectrometry to identify the accumulated ubiquitinated proteins in UCHL5 C88A expressing cells which are mostly distinct from those identified in USP14 C114A expressing cells. Among the identified proteins are well established proteasome substrates and proteasome subunits. Besides β-catenin, we also verified with immunoblotting that UCHL5 C88A inhibits its own deubiquitination and USP14 C114A inhibits deubiquitination of two proteasomal subunits PSMC1 and PSMD4. Together our data suggest that USP14 and UCHL5 can deubiquitinate distinct substrates at the proteasome and regulate the ubiquitination of the proteasome itself which is tightly linked to its function.

Phosphorylation of Glutamine Synthetase on Threonine 301 Contributes to Its Inactivation During Epilepsy

The astrocyte-specific enzyme glutamine synthetase (GS), which catalyzes the amidation of glutamate to glutamine, plays an essential role in supporting neurotransmission and in limiting NH₄⁺ toxicity. Accordingly, deficits in GS activity contribute to epilepsy and neurodegeneration. Despite its central role in brain physiology, the mechanisms that regulate GS activity are poorly defined. Here, we demonstrate that GS is directly phosphorylated on threonine residue 301 (T301) within the enzyme’s active site by cAMP-dependent protein kinase (PKA). Phosphorylation of T301 leads to a dramatic decrease in glutamine synthesis. Enhanced T301 phosphorylation was evident in a mouse model of epilepsy, which may contribute to the decreased GS activity seen during this trauma. Thus, our results highlight a novel molecular mechanism that determines GS activity under both normal and pathological conditions.

Mouse Red Blood Cell-Mediated Rare Xenobiotic Phosphorylation of a Drug Molecule Not Intended to Be a Kinase Substrate

Phosphorylation of xenobiotics is rare, probably owing to a strong evolutionary pressure against it. This rarity may have attracted more attention recently as a result of intentionally designed kinase-substrate analogs that depend on kinase-catalyzed activation to form phosphorylated active drugs. We report a rare phosphorylated metabolite observed unexpectedly in mouse plasma samples after an oral dose of a Tankyrase inhibitor that was not intended to be a kinase substrate, i.e., (S)-2-(4-(6-(3,4-dimethylpiperazin-1-yl)-4-methylpyridin-3-yl)phenyl)-8-(hydroxymethyl)quinazolin-4(3H)-one (AZ2381). The phosphorylated metabolite was not generated in mouse hepatocytes. In vitro experiments showed that the phosphorylation of AZ2381 occurred in mouse whole blood with heparin as anticoagulant but not in mouse plasma. The phosphorylated metabolite was also produced in rat, dog, and human blood, albeit at lower yields than in mouse. Divalent metal ions are required for the phosphorylation since the reaction is inhibited by the metal chelator EDTA. Further investigations with different cellular fractions of mouse blood revealed that the phosphorylation of AZ2381 was mediated by erythrocytes but did not occur with leukocytes. The levels of ¹⁸O incorporation into the phosphorylated metabolite when inorganic ¹⁸O₄-phosphate and γ-¹⁸O₄-ATP were added to the mouse blood incubations separately suggested that the phosphoryl transfer was from inorganic phosphate rather than ATP. It remains unclear which enzyme present in red blood cells is responsible for this rare phosphorylation.

Discovery of Novel DNA Gyrase Inhibiting Spiropyrimidinetriones: Benzisoxazole Fusion with N-Linked Oxazolidinone Substituents Leading to a Clinical Candidate (ETX0914)

A novel class of bacterial type-II topoisomerase inhibitor displaying a spiropyrimidinetrione architecture fused to a benzisoxazole scaffold shows potent activity against Gram-positive and fastidious Gram-negative bacteria. Here, we describe a series of N-linked oxazolidinone substituents on the benzisoxazole that improve upon the antibacterial activity of initially described compounds of the class, show favorable PK properties, and demonstrate efficacy in an in vivo Staphylococcus aureus infection model. Inhibition of the topoisomerases DNA gyrase and topoisomerase IV from both Gram-positive and a Gram-negative organisms was demonstrated. Compounds showed a clean in vitro toxicity profile, including no genotoxicity and no bone marrow toxicity at the highest evaluated concentrations or other issues that have been problematic for some fluoroquinolones. Compound 1u was identified for advancement into human clinical trials for treatment of uncomplicated gonorrhea based on a variety of beneficial attributes including the potent activity and the favorable safety profile.

Inhibition of Neisseria gonorrhoeae Type II Topoisomerases by the Novel Spiropyrimidinetrione AZD0914

We characterized the inhibition of Neisseria gonorrhoeae type II topoisomerases gyrase and topoisomerase IV by AZD0914 (AZD0914 will be henceforth known as ETX0914 (Entasis Therapeutics)), a novel spiropyrimidinetrione antibacterial compound that is currently in clinical trials for treatment of drug-resistant gonorrhea. AZD0914 has potent bactericidal activity against N. gonorrhoeae, including multidrug-resistant strains and key Gram-positive, fastidious Gram-negative, atypical, and anaerobic bacterial species (Huband, M. D., Bradford, P. A., Otterson, L. G., Basrab, G. S., Giacobe, R. A., Patey, S. A., Kutschke, A. C., Johnstone, M. R., Potter, M. E., Miller, P. F., and Mueller, J. P. (2014) In Vitro Antibacterial Activity of AZD0914: A New Spiropyrimidinetrione DNA Gyrase/Topoisomerase Inhibitor with Potent Activity against Gram-positive, Fastidious Gram-negative, and Atypical Bacteria. Antimicrob. Agents Chemother. 59, 467-474). AZD0914 inhibited DNA biosynthesis preferentially to other macromolecules in Escherichia coli and induced the SOS response to DNA damage in E. coli. AZD0914 stabilized the enzyme-DNA cleaved complex for N. gonorrhoeae gyrase and topoisomerase IV. The potency of AZD0914 for inhibition of supercoiling and the stabilization of cleaved complex by N. gonorrhoeae gyrase increased in a fluoroquinolone-resistant mutant enzyme. When a mutation, conferring mild resistance to AZD0914, was present in the fluoroquinolone-resistant mutant, the potency of ciprofloxacin for inhibition of supercoiling and stabilization of cleaved complex was increased greater than 20-fold. In contrast to ciprofloxacin, religation of the cleaved DNA did not occur in the presence of AZD0914 upon removal of magnesium from the DNA-gyrase-inhibitor complex. AZD0914 had relatively low potency for inhibition of human type II topoisomerases α and β.

Rational design of inhibitors of the bacterial cell wall synthetic enzyme GlmU using virtual screening and lead-hopping

An aminoquinazoline series targeting the essential bacterial enzyme GlmU (uridyltransferase) were previously reported (Biochem. J.2012, 446, 405). In this study, we further explored SAR through a combination of traditional medicinal chemistry and structure-based drug design, resulting in a novel scaffold (benzamide) with selectivity against protein kinases. Virtual screening identified fragments that could be fused into the core scaffold, exploiting additional binding interactions and thus improving potency. These efforts resulted in a hybrid compound with target potency increased by a 1000-fold, while maintaining selectivity against selected protein kinases and an improved level of solubility and protein binding. Despite these significant improvements no significant antibacterial activity was yet observed within this class.

Screening-based discovery of the first novel ATP competitive inhibitors of the Staphylococcus aureus essential enzyme UMP kinase

UMP kinase (PyrH) is an essential enzyme found only in bacteria, making it ideal as a target for the discovery of antibacterials. To identify inhibitors of PyrH, an assay employing Staphylococcus aureus PyrH coupled to pyruvate kinase/lactate dehydrogenase was developed and was used to perform a high throughput screen. A validated aminopyrimidine series was identified from screening. Kinetic characterization of this aminopyrimidine indicated it was a competitive inhibitor of ATP. We have shown that HTS can be used to identify potential leads for this novel target, the first ATP competitive inhibitor of PyrH reported.

In vivo validation of thymidylate kinase (TMK) with a rationally designed, selective antibacterial compound

There is an urgent need for new antibacterials that pinpoint novel targets and thereby avoid existing resistance mechanisms. We have created novel synthetic antibacterials through structure-based drug design that specifically target bacterial thymidylate kinase (TMK), a nucleotide kinase essential in the DNA synthesis pathway. A high-resolution structure shows compound TK-666 binding partly in the thymidine monophosphate substrate site, but also forming new induced-fit interactions that give picomolar affinity. TK-666 has potent, broad-spectrum Gram-positive microbiological activity (including activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus), bactericidal action with rapid killing kinetics, excellent target selectivity over the human ortholog, and low resistance rates. We demonstrate in vivo efficacy against S. aureus in a murine infected-thigh model. This work presents the first validation of TMK as a compelling antibacterial target and provides a rationale for pursuing novel clinical candidates for treating Gram-positive infections through TMK.

Bacterial DNA replication enzymes as targets for antibacterial drug discovery

INTRODUCTION

The bacterial replisome is composed of a large number of enzymes, which work in exquisite coordination to accomplish chromosomal replication. Effective inhibition inside the bacterial cell of any of the 'essential' enzymes of the DNA replication pathway should be detrimental to cell survival.

AREAS COVERED

This review covers DNA replication enzymes that have been shown to have a potential for delivering antibacterial compounds or drug candidates including: type II topoisomerases, a clinically validated target family, and DNA ligase, which has yielded inhibitors with in vivo efficacy. A few of the 'replisome' enzymes that are structurally and functionally well characterized and have been subjects of antibacterial discovery efforts are also discussed.

EXPERT OPINION

Identification of several essential genes in the bacterial replication pathway raised hopes that targeting these gene products would lead to novel antibacterials. However, none of these novel, single gene targets have delivered antibacterial drug candidates into clinical trials. This lack of productivity may be due to the target properties and inhibitor identification approaches employed. For DNA primase, DNA helicase and other replisome targets, with the exception of DNA ligase, the exploitation of structure for lead generation has not been tested to the same extent that it has for DNA gyrase. Utilization of structural information should be considered to augment HTS efforts and initiate fragment-based lead generation. The complex protein-protein interactions involved in regulation of replication may explain why biochemical approaches have been less productive for some replisome targets than more independently functioning targets such as DNA ligase or DNA gyrase.

Treatment of log yard runoff using a r-circulating sand filtration process

A re-circulating filtration process using oxide-coated sand successfully removed COD and turbidity from log yard runoff. After passing only one pore volume of the runoff through the sand column, 72% COD was removed. The 2.4% Fe and Al oxide coating on the sand contributed to better COD removal than was obtained when the sand was stripped of oxide coating (86% versus 52%, respectively), at least initially before saturation of adsorption sites on the oxide coating occurred. The best COD removal performance came from conditioned sand. This sand, from the same original source and identical to the oxide-coated sand used in all experiments, came from an existing experimental sand column that had been treating log yard runoff for 1 year. The "conditioning" resulted in the sand having a higher TOC content (0.26% wt) and smaller particle sizes. This sand was able to consistently remove 80% COD from repeated batches of log yard runoff with strengths up to 3690 mg l(-1).

Characterization of proteins in the outer membrane preparation of a murine pathogen, Helicobacter bilis

Helicobacter bilis is a bacterial pathogen associated with multifocal hepatitis and inflammatory bowel disease in certain strains of mice. This bacterium colonizes the liver, bile, and lower intestine in mice and has also been isolated from a wide spectrum of laboratory animals. In this study, proteins present in the outer membrane preparation (OMP) of four H. bilis strains isolated from a mouse, a dog, a rat, and a gerbil were characterized and compared with that of Helicobacter pylori, a human gastric pathogen. All four H. bilis strains had similar OMP protein profiles that were distinct from those of H. pylori. Immunoblotting demonstrated that OMP proteins from H. bilis and H. pylori have little cross-reactivity, except for their flagellins. Nine major immunogenic polypeptides were present in the H. bilis OMPs. By using two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, five heat-modifiable proteins with molecular masses of 82, 66, 52, 47 and 37 kDa were identified. The N-terminal sequences of the 46- and 47-kDa OMP proteins had no homology with protein sequences available in public databases. These results indicate that H. bilis has a conserved, unique OMP protein profile that is distinct from those of H. pylori.

Comparative genomics of Helicobacter pylori: analysis of the outer membrane protein families

The two complete genomic sequences of Helicobacter pylori J99 and 26695 were used to compare the paralogous families (related genes within one genome, likely to have related function) of genes predicted to encode outer membrane proteins which were present in each strain. We identified five paralogous gene families ranging in size from 3 to 33 members; two of these families contained members specific for either H. pylori J99 or H. pylori 26695. Most orthologous protein pairs (equivalent genes between two genomes, same function) shared considerable identity between the two strains. The unusual set of outer membrane proteins and the specialized outer membrane may be a reflection of the adaptation of H. pylori to the unique gastric environment where it is found. One subfamily of proteins, which contains both channel-forming and adhesin molecules, is extremely highly related at the sequence level and has likely arisen due to ancestral gene duplication. In addition, the largest paralogous family contained two essentially identical pairs of genes in both strains. The presence and genomic organization of these two pairs of duplicated genes were analyzed in a panel of independent H. pylori isolates. While one pair was present in every strain examined, one allele of the other pair appeared partially deleted in several isolates.

Audit of emergency medical admissions during the winter 1997/1998

OBJECTIVES

To test the hypothesis that a significant cause of rising medical admissions over the Christmas and New Year period is the failure of social and medical systems which support patients at home for most of the year; and to understand the reasons for admission during the winter months of an at risk population and to identify possible avoidable admissions.

DESIGN

Structured interviews were conducted with patients within 48 hours of admission to collect information on home circumstances and contact with social, medical and primary care in the year prior to admission. In cases where the patient was unable to provide this information, case notes and nursing notes were reviewed. Discharge diagnosis was recorded at the end of the study period.

SUBJECTS

Five hundred and thirty nine patients defined as an "at risk group" who were admitted to hospital as emergency medical admissions between 1st December 1997 and 31st January 1998.

RESULTS

Subjects were predominantly female (58%). The major diagnostic groups were cardiac (27%) and respiratory (22%). Respondents indicated no change in primary care in the period preceding their admission, with the exception of day centre support. Sixty seven percent of patients fully interviewed received help from carers, friends or relatives with daily tasks and only seven (3%) reported receiving less input prior to admission. Forty five percent of these patients had seen a GP within the month prior to their admission.

CONCLUSIONS

The study results showed no breakdown in either social or family support. In the group interviewed, the proportion who had experienced any decrease in social support during the period prior to admission was very small.

Helicobacter pylori physiology predicted from genomic comparison of two strains

Helicobacter pylori is a gram-negative bacteria which colonizes the gastric mucosa of humans and is implicated in a wide range of gastroduodenal diseases. This paper reviews the physiology of this bacterium as predicted from the sequenced genomes of two unrelated strains and reconciles these predictions with the literature. In general, the predicted capabilities are in good agreement with reported experimental observations. H. pylori is limited in carbohydrate utilization and will use amino acids, for which it has transporter systems, as sources of carbon. Energy can be generated by fermentation, and the bacterium possesses components necessary for both aerobic and anaerobic respiration. Sulfur metabolism is limited, whereas nitrogen metabolism is extensive. There is active uptake of DNA via transformation and ample restriction-modification activities. The cell contains numerous outer membrane proteins, some of which are porins or involved in iron uptake. Some of these outer membrane proteins and the lipopolysaccharide may be regulated by a slipped-strand repair mechanism which probably results in phase variation and plays a role in colonization. In contrast to a commonly held belief that H. pylori is a very diverse species, few differences were predicted in the physiology of these two unrelated strains, indicating that host and environmental factors probably play a significant role in the outcome of H. pylori-related disease.

Characterization of a post-translational modification of Campylobacter flagellin: identification of a sero-specific glycosyl moiety

The flagellins of Campylobacter spp. differ antigenically. In variants of C. coli strain VC167, two antigenic flagellin types determined by sero-specific antibodies have been described (termed T1 and T2). Post-translational modification has been suggested to be responsible for T1 and T2 epitopes, and, using mild periodate treatment and biotin hydrazide labelling, flagellin from both VC167-T1 and T2 were shown to be glycosylated. Glycosylation was also shown to be present on other Campylobacter flagellins. The ability to label all Campylobacter flagellins examined with the lectin LFA demonstrated the presence of a terminal sialic acid moiety. Furthermore, mild periodate treatment of the flagellins of VC167 eliminated reactivity with T1 and T2 specific antibodies LAH1 and LAH2, respectively, and LFA could also compete with LAH1 and LAH2 antibodies for binding to their respective flagellins. These data implicate terminal sialic acid as part of the LAH strain-specific epitopes. However, using mutants in genes affecting LAH serorecognition of flagellin it was demonstrated that sialic acid alone is not the LAH epitope. Rather, the epitope(s) is complex, probably involving multiple glycosyl and/or amino acid residues.

Identification and characterization of genes required for post-translational modification of Campylobacter coli VC167 flagellin

Two genes have been identified in Campylobacter coli VC167 which are required for the biosynthesis of post-translational modifications on flagellin proteins. The ptmA gene encodes a protein of predicted M(r) 28,486 which shows significant homology to a family of alcohol dehydrogenases from a variety of bacteria. The ptmB gene encodes a protein of predicted M(r) 26,598 with significant homology to CMP-N-acetylneuraminic acid synthetase enzymes involved in sialic acid capsular biosynthesis in Neisseria meninigitidis and Escherichia coli K1. Site-specific mutation of either ptmA or ptmB caused loss of reactivity with antisera specific to the post-translational modifications and a change in the isoelectric focusing fingerprints relative to the parent strains. Mutation of ptmB, but not of ptmA, caused a change in apparent M(r) of the flagellin subunit in SDS-PAGE gels. The ptmA and ptmB genes are present in other strains of Campylobacter. In a rabbit model the ptmA mutant showed a reduced ability to elicit protection against subsequent challenge with heterologous strains of the same Lior serotype compared to the parental wild-type strain. This suggests that the surface-exposed post-translational modifications may play a significant role in the protective immune response.

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.

Isolation and characterization of a conserved porin protein from Helicobacter pylori

Helicobacter pylori is a causative agent of gastritis in humans and is correlated with gastric ulcer formation. Infections with this bacterium have proven difficult to treat with antimicrobial agents. To better understand how this bacterium transports compounds such as antimicrobial agents across its outer membrane, identification of porin proteins is important. We have recently identified a family of H. pylori porins (HopA to HopD) (M. M. Exner, P. Doig, T. J. Trust, and R. E. W. Hancock, Infect. Immun. 63:1567-1572, 1995). Here, we report on an unrelated porin species (HopE) from this bacterium. This protein had a apparent molecular mass of 31 kDa and was seen to form 50- and 90-kDa aggregates that were designated putative dimeric and trimeric forms, respectively. The protein was purified to homogeneity and, with a model planar lipid membrane system, was shown to act as a nonselective pore with a single channel conductance in 1.0 M KCl of 1.5 nS, similarly to other bacterial nonspecific porins. An internal peptide sequence of HopE shared homology with the P2 porin of Haemophilus influenzae. HopE was also shown to be antigenic in vivo as assessed by sera taken from H. pylori-infected individuals and was immunologically conserved with both patient sera and specific monoclonal antibodies. From these data, it appears that HopE is a major nonselective porin of H. pylori. The implications of these findings are discussed.

Stimulation of interleukin-8 production in epithelial cell lines by Helicobacter pylori

Following exposure to Helicobacter pylori cells, epithelial cell lines secreted interleukin-6 (IL-6) and IL-8 but not tumor necrosis factor alpha. Purified IL-6 alone did not stimulate IL-8 production from the cell lines tested, indicating that IL-6 was not an intermediary in IL-8 induction. Enhanced IL-8 secretion occurred in a time- and dose-dependent manner. None of 12 antibiotics tested exhibited a significant effect on IL-8-inducing activity, suggesting that preformed antigens were responsible for stimulating IL-8 secretion in vitro. Live bacterial cells caused the highest level of stimulation. Proteinase-digested and heated (56 or 100 degrees C) cells had significantly reduced stimulatory activities. Purified H. pylori lipopolysaccharide, but not exopolysaccharide, stimulated low-level secretion of IL-8, but only at high concentrations, while a water-extracted H. pylori antigen preparation was strongly stimulatory for HEp-2 cells. No reduction in IL-8-stimulatory activity was observed for H. pylori mutants negative for urease activity, production of a major lipoprotein, and motility. The noncytotoxic strain CCUG 915 stimulated lower IL-8 levels than other isolates. However, the otherwise isogenic cytotoxin-negative mutant 17874 delta vacA (S. H. Phadnis, D. Ilver, L. Janzon, S. Normark, and T. U. Westblom, Infect. Immun. 62:1557-1565, 1994) had the same IL-8-stimulatory ability as the parent strain, suggesting that surface proteins other than the vacuolating cytotoxin are involved in IL-8 stimulation.

Isolation and characterization of a family of porin proteins from Helicobacter pylori

Two-dimensional gel electrophoresis was used to identify heat-modifiable outer membrane proteins, which were candidates for porins, from Helicobacter pylori membrane preparations. Four such proteins with apparent molecular masses of 48, 49, 50, and 67 kDa were isolated. The four proteins copurified together after selective detergent solubilizations followed by anion-exchange chromatography, and each protein was ultimately purified to homogeneity by gel purification. These proteins were then tested for pore-forming ability with a planar lipid bilayer model membrane system. All four proteins appeared to be present as monomers, and they formed pores with low single-channel conductances in 1.0 M KCl of 0.36, 0.36, 0.30, and 0.25 nS, respectively, for the 48-, 49-, 50-, and 67-kDa proteins which we propose to designate HopA, HopB, HopC, and HopD. N-terminal amino acid sequence analyses showed a high degree of homology among all four proteins, and it appears that these proteins constitute a family of related porins in H. pylori.

Isolation of motile and non-motile insertional mutants of Campylobacter jejuni: the role of motility in adherence and invasion of eukaryotic cells

A method of insertional mutagenesis for naturally transformable organisms has been adapted from Haemophilus influenzae and applied to the study of the pathogenesis of Campylobacter jejuni. A series of kanamycin-resistant insertional mutants of C. jejuni 81-176 has been generated and screened for loss of ability to invade INT407 cells. Eight noninvasive mutants were identified which showed 18-200-fold reductions in the level of invasion compared with the parent. Three of these eight show defects in motility, and five are fully motile. The three mutants with motility defects were further characterized to evaluate the method. One mutant, K2-32, which is non-adherent and non-invasive, has an insertion of the kanamycin-resistance cassette into the flaA flagellin gene and has greatly reduced motility and a truncated flagellar filament typical of flaA mutants. The adherent non-invasive mutants K2-37 and K2-55 are phenotypically paralysed, i.e. they have a full-length flagellar filament but are non-motile. All three mutants show an aberration in flagellar structure at the point at which the filament attaches to the cell. Mutants K2-37 and K2-55 represent overlapping deletions affecting the same gene, termed pflA (paralysed flagella). This gene encodes a predicted protein of 788 amino acid residues and a molecular weight of 90,977 with no significant homology to known proteins. Site-specific insertional mutants into this open reading frame result in the same paralysed flagellar phenotype and the same invasion defects as the original mutants. The differences in adherence between the two classes of flagellar mutant suggest that flagellin can serve as a secondary adhesion, although other adhesins mediate a motility-dependent internalization process. Characterization of the mutants at the molecular level and in animal models should further contribute to our understanding of the pathogenicity of these organisms.

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.

Distribution of surface-exposed and non-accessible amino acid sequences among the two major structural domains of the S-layer protein of Aeromonas salmonicida

The tetragonally arranged crystalline surface protein array (A-layer) of the fish pathogenic bacterium Aeromonas salmonicida is a virulence factor. Circular dichroism studies in the presence or absence of 0.1% sodium dodecyl sulfate showed that the secondary structure of A-protein, and its 39,439 molecular weight amino-terminal trypsin-resistant peptide, were altered. In both cases alpha-helix was increased significantly at the expense of beta-structure when SDS was added. Western and dot immunoblotting, immuno-microscopy and enzyme-linked immunosorbent assay with monospecific polyclonal antiserum and eight monoclonal antibodies specific for epitopes exposed on the surface of native A-layer showed that the 481 residue A-protein subunit and the surface of A-layer were conserved antigenically. Mimeotope analysis of nonapeptides representing the sequence of A-protein allowed identification of 146 residues in presumed linear epitopes accessible on the surface of A-layer. Inaccessible or non-epitopic residues accounted for 70% of the protein. The majority of inaccessible residues were in the N-terminal 301 residues of A-protein. Dispersed among these were 65 surface-accessible residues in five linear epitope clusters illustrating the complex folding of this major structural domain of A-protein. The C-terminal 180 residues carried fewer linear epitopes but contained the major region of A-layers surface-accessible sequence, including four linear epitopes in predominantly hydrophobic sequence. Four A-layer surface-binding monoclonal antibodies also bound to this minor structural domain, although the epitopes of only two were identified by mimeotope analysis. The epitopes of six A-layer surface-binding monoclonals could not be identified, suggesting that A-layer may also contain conformation dependent surface epitopes.