Protein I: structure, function, and genetics

Pathogenic Neisseria Bind the Complement Protein CFHR5 via Outer Membrane Porins

Neisseria meningitidis and Neisseria gonorrhoeae are important human pathogens that have evolved to bind the major negative regulator of the complement system, complement factor H (CFH). However, little is known about the interaction of pathogens with CFH-related proteins (CFHRs) which are structurally similar to CFH but lack the main complement regulatory domains found in CFH. Insights into the role of CFHRs have been hampered by a lack of specific reagents. We generated a panel of CFHR-specific monoclonal antibodies and demonstrated that CFHR5 was bound by both pathogenic Neisseria spp. We showed that CFHR5 bound to PorB expressed by both pathogens in the presence of sialylated lipopolysaccharide and enhanced complement activation on the surface of N. gonorrhoeae. Our study furthered our understanding of the interactions of CFHRs with bacterial pathogens and revealed that CFHR5 bound the meningococcus and gonococcus via similar mechanisms.

Development of Food Group Tree-Based Analysis and Its Association with Non-Alcoholic Fatty Liver Disease (NAFLD) and Co-Morbidities in a South Indian Population: A Large Case-Control Study

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a global problem growing in parallel to the epidemics of obesity and diabetes, with South Asians being particularly susceptible. Nutrition and behaviour are important modifiers of the disease; however, studies to date have only described dietary patterns and nutrients associated with susceptibility to NAFLD.

METHODS

This cross-sectional case-control study included 993 NAFLD patients and 973 healthy controls from Trivandrum (India). Dietary data was collected using a locally validated food frequency questionnaire. A tree-based classification categorised 2165 ingredients into three levels (food groups, sub-types, and cooking methods) and intakes were associated with clinical outcomes.

RESULTS

NAFLD patients had significantly higher consumption of refined rice, animal fat, red meat, refined sugar, and fried foods, and had lower consumption of vegetables, pulses, nuts, seeds, and milk compared to controls. The consumption of red meat, animal fat, nuts, and refined rice was positively associated with NAFLD diagnosis and the presence of fibrosis, whereas consumption of leafy vegetables, fruits, and dried pulses was negatively associated. Fried food consumption was positively associated with NAFLD, whilst boiled food consumption had a negative association. Increased consumption of animal fats was associated with diabetes, hypertension, and cardiovascular outcomes among those with NAFLD, whereas consumption of wholegrain rice was negatively associated with these clinical-related outcomes.

CONCLUSIONS

The tree-based approach provides the first comprehensive method of classifying food intakes to enable the identification of specific dietary factors associated with NAFLD and related clinical outcomes. This could inform culturally sensitive dietary guidelines to reduce risk of NAFLD development and/or its progression.

Impact of Species Diversity on the Design of RNA-Based Diagnostics for Antibiotic Resistance in Neisseria gonorrhoeae

Quantitative assessment of antibiotic-responsive RNA transcripts holds promise for a rapid point-of-care (POC) diagnostic tool for antimicrobial susceptibility testing. These assays aim to distinguish susceptible and resistant isolates by transcriptional differences upon drug exposure. However, an often-overlooked dimension of designing these tests is that the genetic diversity within a species may yield differential transcriptional regulation independent of resistance phenotype. Here, we use a phylogenetically diverse panel of Neisseria gonorrhoeae and transcriptome profiling coupled with reverse transcription-quantitative PCR to test this hypothesis, to identify azithromycin responsive transcripts and evaluate their potential diagnostic value, and to evaluate previously reported diagnostic markers for ciprofloxacin resistance (porB and rpmB). Transcriptome profiling confirmed evidence of genetic distance and population structure impacting transcriptional response to azithromycin. Taking this into account, we found azithromycin-responsive transcripts overrepresented in susceptible strains compared to resistant strains and selected four candidate diagnostic transcripts (rpsO, rplN, omp3, and NGO1079) that were the most significantly differentially regulated between phenotypes across drug exposure. RNA signatures for these markers categorically predicted resistance in 19/20 cases, with the one incorrect categorical assignment for an isolate at the threshold of reduced susceptibility. Finally, we found that porB and rpmB expression were not uniformly diagnostic of ciprofloxacin resistance in a panel of isolates with unbiased phylogenetic sampling. Overall, our results suggest that RNA signatures as a diagnostic tool are promising for future POC diagnostics; however, development and testing should consider representative genetic diversity of the target pathogen.

Gonorrhea - an evolving disease of the new millennium

Etiology, transmission and protection: Neisseria gonorrhoeae (the gonococcus) is the etiological agent for the strictly human sexually transmitted disease gonorrhea. Infections lead to limited immunity, therefore individuals can become repeatedly infected. Pathology/symptomatology: Gonorrhea is generally a non-complicated mucosal infection with a pustular discharge. More severe sequellae include salpingitis and pelvic inflammatory disease which may lead to sterility and/or ectopic pregnancy. Occasionally, the organism can disseminate as a bloodstream infection. Epidemiology, incidence and prevalence: Gonorrhea is a global disease infecting approximately 60 million people annually. In the United States there are approximately 300, 000 cases each year, with an incidence of approximately 100 cases per 100,000 population. Treatment and curability: Gonorrhea is susceptible to an array of antibiotics. Antibiotic resistance is becoming a major problem and there are fears that the gonococcus will become the next "superbug" as the antibiotic arsenal diminishes. Currently, third generation extended-spectrum cephalosporins are being prescribed. Molecular mechanisms of infection: Gonococci elaborate numerous strategies to thwart the immune system. The organism engages in extensive phase (on/off switching) and antigenic variation of several surface antigens. The organism expresses IgA protease which cleaves mucosal antibody. The organism can become serum resistant due to its ability to sialylate lipooligosaccharide in conjunction with its ability to subvert complement activation. The gonococcus can survive within neutrophils as well as in several other lymphocytic cells. The organism manipulates the immune response such that no immune memory is generated which leads to a lack of protective immunity.

Reference map and comparative proteomic analysis of Neisseria gonorrhoeae displaying high resistance against spectinomycin

A proteome reference map of Neisseria gonorrhoeae was successfully established using two-dimensional gel electrophoresis in conjunction with matrix-assisted laser desorption ionization-time of flight mass spectrometry. This map was further applied to compare protein expression profiles of high-level spectinomycin-resistant (clinical isolate) and -susceptible (reference strain) N. gonorrhoeae following treatment with subminimal inhibitory concentrations (subMICs) of spectinomycin. Approximately 200 protein spots were visualized by Coomassie brilliant blue G-250 staining and 66 spots representing 58 unique proteins were subsequently identified. Most of the identified proteins were analysed as cytoplasmic proteins and belonged to the class of energy metabolism. Comparative proteomic analysis of whole protein expression of susceptible and resistant gonococci showed up to 96% similarity while eight proteins were found to be differentially expressed in the resistant strain. In the presence of subMICs of spectinomycin, it was found that 50S ribosomal protein L7/L12, an essential component for ribosomal translocation, was upregulated in both strains, ranging from 1.5- to 3.5-fold, suggesting compensatory mechanisms of N. gonorrhoeae in response to antibiotic that inhibits protein synthesis. Moreover, the differential expression of proteins involved in energy metabolism, amino acid biosynthesis, and the cell envelope was noticeably detected, indicating significant cellular responses and adaptation against antibiotic stress. Such knowledge provides valuable data, not only fundamental proteomic data, but also knowledge of the mode of action of antibiotic and secondary target proteins implicated in adaptation and compensatory mechanisms.

Functional comparison of the binding of factor H short consensus repeat 6 (SCR 6) to factor H binding protein from Neisseria meningitidis and the binding of factor H SCR 18 to 20 to Neisseria gonorrhoeae porin

Both Neisseria meningitidis and Neisseria gonorrhoeae recruit the alternative pathway complement inhibitory protein factor H (fH) to their surfaces to evade complement-dependent killing. Meningococci bind fH via fH binding protein (fHbp), a surface-exposed lipoprotein that is subdivided into three variant families based on one classification scheme. Chimeric proteins that comprise contiguous domains of fH fused to murine Fc were used to localize the binding site for all three fHbp variants on fH to short consensus repeat 6 (SCR 6). As expected, fH-like protein 1 (FHL-1), which contains fH SCR 6, also bound to fHbp-expressing meningococci. Using site-directed mutagenesis, we identified histidine 337 and histidine 371 in SCR 6 as important for binding to fHbp. These findings may provide the molecular basis for recent observations that demonstrated human-specific fH binding to meningococci. Differences in the interactions of fHbp variants with SCR 6 were evident. Gonococci bind fH via their porin (Por) molecules (PorB.1A or PorB.1B); sialylation of lipooligosaccharide enhances fH binding. Both sialylated PorB.1B- and (unsialylated) PorB.1A-bearing gonococci bind fH through SCR 18 to 20; PorB.1A can also bind SCR 6, but only weakly, as evidenced by a low level of binding of FHL-1 relative to that of fH. Using isogenic strains expressing either meningococcal fHbp or gonococcal PorB.1B, we discovered that strains expressing gonococcal PorB.1B in the presence of sialylated lipooligosaccharide bound more fH, more effectively limited C3 deposition, and were more serum resistant than their isogenic counterparts expressing fHbp. Differences in fH binding to these two related pathogens may be important for modulating their individual responses to host immune attack.

RpoH mediates the expression of some, but not all, genes induced in Neisseria gonorrhoeae adherent to epithelial cells

Neisseria gonorrhoeae (gonococcus [GC]), is highly adapted to the human host, the only known reservoir for gonococcal infection. However, since it is sexually transmitted, infection of a new host likely requires a regulatory response on the part of the gonococcus to respond to this significant change in environment. We previously showed that adherence of gonococci to epithelial cells results in changes of gene expression in the bacteria that presumably prepare them for subsequent steps in the infection process. Expression of the heat shock sigma factor gene, rpoH, was shown to be important for the invasion step, as gonococci depleted for rpoH were reduced in their ability to invade epithelial cells. Here, we show that of the genes induced in adherent gonococci, two are part of the gonococcal RpoH regulon. When RpoH is depleted, expression of these genes is no longer induced by host cell contact, indicating that RpoH is mediating the host cell induction response of these genes. One RpoH-dependent gene, NGO0376, is shown to be important for invasion of epithelial cells, consistent with earlier observations that RpoH is necessary for this step of infection. Two genes, NGO1684 and NGO0340, while greatly induced by host cell contact, were found to be RpoH independent, indicating that more than one regulator is involved in the response to host cell contact. Furthermore, NGO0340, but not NGO1684, was shown to be important for both adherence and invasion of epithelial cells, suggesting a complex regulatory network in the response of gonococci to contact with host cells.

Global gene expression and the role of sigma factors in Neisseria gonorrhoeae in interactions with epithelial cells

Like many bacterial pathogens, Neisseria gonorrhoeae must adapt to environmental changes in order to successfully colonize and proliferate in a new host. Modulation of gene expression in response to environmental signals is an efficient mechanism used by bacteria to achieve this goal. Using DNA microarrays and a tissue culture model for gonococcal infection, we examined global changes in gene expression in N. gonorrhoeae in response to adherence to host cells. Among those genes induced upon adherence to human epithelial cells in culture was rpoH, which encodes a homolog of the heat shock sigma factor, sigma(32) (RpoH), as well as genes of the RpoH regulon, groEL and groES. Attempts to construct an rpoH null mutant in N. gonorrhoeae were unsuccessful, suggesting that RpoH is essential for viability of N. gonorrhoeae. The extracytoplasmic sigma factor, RpoE (sigma(E)), while known to regulate rpoH in other bacteria, was found not to be necessary for the up-regulation of rpoH in gonococci upon adherence to host cells. To examine the role of RpoH in host cell interactions, an N. gonorrhoeae strain conditionally expressing rpoH was constructed. The results of our experiments showed that while induction of rpoH expression is not necessary for adherence of gonococci to epithelial cells, it is important for the subsequent invasion step, as gonococci depleted for rpoH invade cells two- to threefold less efficiently than a wild-type strain. Taken together, these results indicate that sigma(32), but not sigma(E), is important for the response of gonococci in the initial steps of an infection.

Identification of ZipA, a signal recognition particle-dependent protein from Neisseria gonorrhoeae

A genetic screen designed to identify proteins that utilize the signal recognition particle (SRP) for targeting in Escherichia coli was used to screen a Neisseria gonorrhoeae plasmid library. Six plasmids were identified in this screen, and each is predicted to encode one or more putative cytoplasmic membrane (CM) proteins. One of these, pSLO7, has three open reading frames (ORFs), two of which have no similarity to known proteins in GenBank other than sequences from the closely related N. meningitidis. Further analyses showed that one of these, SLO7ORF3, encodes a protein that is dependent on the SRP for localization. This gene also appears to be essential in N. gonorrhoeae since it was not possible to generate null mutations in the gene. Although appearing unique to Neisseria at the DNA sequence level, SLO7ORF3 was found to share some features with the cell division gene zipA of E. coli. These features included similar chromosomal locations (with respect to linked genes) as well as similarities in the predicted protein domain structures. Here, we show that SLO7ORF3 can complement an E. coli conditional zipA mutant and therefore encodes a functional ZipA homolog in N. gonorrhoeae. This observation is significant in that it is the first ZipA homolog identified in a non-rod-shaped organism. Also interesting is that this is the fourth cell division protein (the others are FtsE, FtsX, and FtsQ) shown to utilize the SRP for localization, which may in part explain why the genes encoding the three SRP components are essential in bacteria.

The outer membrane localization of the Neisseria gonorrhoeae MsrA/B is involved in survival against reactive oxygen species

The PilB protein of Neisseria gonorrhoeae has been reported to be involved in the regulation of pilin gene transcription, but it also possesses significant homology to the peptide methionine sulfoxide reductase family of enzymes, specifically MsrA and MsrB from Escherichia coli. MsrA and MsrB in E. coli are able to reduce methionine sulfoxide residues in proteins to methionines. In addition, the gonococcal PilB protein encodes for both MsrA and MsrB activity associated with the repair of oxidative damage to proteins. In this work, we demonstrate that the PilB protein of Neisseria gonorrhoeae is not involved in pilus expression. Additionally, we show that wild-type N. gonorrhoeae produces two forms of this polypeptide, one of which contains a signal sequence and is secreted from the bacterial cytoplasm to the outer membrane; the other lacks a signal sequence and is cytoplasmic. Furthermore, we show that the secreted form of the PilB protein is involved in survival in the presence of oxidative damage.

Neisseria gonorrhoeae porin modifies the oxidative burst of human professional phagocytes

A hallmark of infection with the gram-negative bacterium Neisseria gonorrhoeae is the local infiltration and subsequent activation of polymorphonuclear neutrophils. Several gonococcal outer membrane proteins are involved in the interaction with and the activation of these phagocytes, including gonococcal porin, the most abundant protein in the outer membrane. Previous work suggests that this porin plays a role in various cellular processes, including inhibiting neutrophils activation and phagosome maturation in professional phagocytes. Here we investigated the ability of porin to modify the oxidative metabolism of human peripheral blood neutrophils and monocytes in response to particulate stimuli (including live gonococci) and soluble agents. The activation of the oxidative metabolism was determined by chemiluminescence amplified with either luminol or lucigenin. We found that treatment of the phagocytes with porin inhibits the release of reactive oxygen species measured as luminol-enhanced chemiluminescence in response to zymosan, latex particles, and gonococci. The engulfment of these particles was not, however, affected by porin treatment. Similar effects of porin on the chemiluminescence response were observed in cytochalasin B-treated neutrophils exposed to the soluble chemotactic peptide N-formylmethionyl-leucyl-phenylalanine. This indicates that porin selectively inhibits granule fusion with those cellular membranes that are in direct contact with porin, namely, the phagosomal and plasma membranes. This porin-induced downregulation of oxidative metabolism may be a potent mechanism by which gonococci modulate oxygen-dependent reactions by activated phagocytes at inflammation sites.

Antigenic and molecular conservation of the gonococcal NspA protein

A low-molecular-weight protein named NspA (neisserial surface protein A) was recently identified in the outer membrane of all Neisseria meningitidis strains tested. Antibodies directed against this protein were shown to protect mice against an experimental meningococcal infection. Hybridization experiments clearly demonstrated that the nspA gene was also present in the genomes of the 15 Neisseria gonorrhoeae strains tested. Cloning and sequencing of the nspA gene of N. gonorrhoeae B2 revealed an open reading frame of 525 nucleotides coding for a polypeptide of 174 amino acid residues, with a calculated molecular weight of 18,316 and a pI of 10.21. Comparison of the predicted amino acid sequence of the NspA polypeptides from the gonococcal strains B2 and FA1090, together with that of the meningococcal strain 608B, revealed an identity of 93%, suggesting that the NspA protein is highly conserved among pathogenic Neisseria strains. The level of identity rose to 98% when only the two gonococcal predicted NspA polypeptides were compared. To evaluate the level of antigenic conservation of the gonococcal NspA protein, monoclonal antibodies (MAbs) were generated. Four of the seven NspA-specific MAbs described in this report recognized their corresponding epitope in 100% of the 51 N. gonorrhoeae strains tested. Radioimmunobinding assays clearly indicated that the gonococcal NspA protein is exposed at the surface of intact cells.

Mechanisms of neisserial serum resistance

Pathogenic Neisseria use a variety of mechanisms to survive the bactericidal action of the complement system. Serum resistance is a crucial virulence factor for the development of severe meningococcal disease, meningococcal meningitis and disseminated gonococcal infection. Furthermore, local inflammation at the site of gonococcal infection exposes the bacteria to moderate concentrations of complement factors. We review current concepts of neisserial serum resistance with emphasis on porins and polysaccharides exposed on the neisserial surface and their interaction with components of normal human serum.

Characterization of a subunit structure and stability of the recombinant porin from Neisseria gonorrhoeae

An outer membrane PIA protein from Neisseria gonorrhoeae strain FA19 was expressed in Escherichia coli and refolded in vitro in the presence of zwitterionic detergent. Its proper folding and subunit organization was confirmed by comparison with the native counterpart. The unfolding of PIA has been investigated using fluorescence spectroscopy and analytical size-exclusion chromatography methods. Analysis of the denaturation pathway of the PIA revealed that it forms an unusually labile quaternary structure. In the presence of 1 M guanidinium chloride (GdmCl) or upon heating up to 50 degrees C, dissociation of the PIA oligomer was observed resulting in the formation of folded monomeric intermediates. Unfolding of monomers occurs at 80 degrees C or in the presence of 4.3 M GdmCl, indicating high intrinsic stability toward both GdmCl and elevated temperatures. Both oligomeric and monomeric forms of PIA exhibited affinity to the hydrophobic probe 1-anilinonaphthalene-8-sulfonic acid (ANS) and bind with Kd=80 and 130 microM, respectively. Denaturation of the PIA completely abolished affinity to ANS, suggesting that hydrophobicity is a property of the folded state of the porin.

Gonococcal invasion of epithelial cells driven by P.IA, a bacterial ion channel with GTP binding properties

The neisserial porin P.I is a GTP binding protein that forms a voltage-gated channel that translocates into mammalian cell membranes and modulates host cell signaling events. Here, we report that P.I confers invasion of the bacterial pathogen Neisseria gonorrhoeae into Chang epithelial cells and that this event is controlled by GTP, as well as other phosphorus-containing compounds. Bacterial invasion was observed only for strains carrying the P.IA subtype of porin, which is typically associated with the development of disseminated neisserial disease, and did not require opacity outer membrane proteins, previously recognized as gonococcal invasins. Allelic replacement studies showed that bacterial invasiveness cotransferred with the P.IA (por1A) gene. Mutation of the P.I-associated protein Rmp did not alter the invasive properties. Cross-linking of labeled GTP to the porin revealed more efficient GTP binding to the P.IA than P.IB porin subtype. GTP binding was inhibited by an excess of unlabeled GTP, ATP, and GDP, as well as inorganic phosphate, but not by UTP or beta-glycerophosphate, fully in line with the respective invasion-inhibitory activities observed for these compounds. The P.IA-mediated cellular invasion may explain the more invasive behavior of P.IA strains in the natural infection and may broaden the basis for the development of a P.I-based gonococcal vaccine.

Gonococcal arthritis

Disseminated gonococcal infection is the most common systemic complication of acute gonorrhea and occurs in 0.5% to 3.0% of patients with untreated mucosal infection. It is also the most common cause of septic arthritis in patients less than 30 years of age. Fortunately, the incidence of gonorrhea is decreasing dramatically in the United States and Western Europe, although it is still high in developing countries. Increasing resistance to antibiotics requires continuous surveillance of antimicrobial susceptibilities to determine the efficacy of current therapeutic measures.

Immunogenicity expressed in patients with bacteraemia of an epitope shared by enterobacterial and neisserial porin proteins

A monoclonal antibody (MAb) against an epitope (Po I) on an Escherichia coli O55 porin protein has shown broad cross-reactivity with other Enterobacteriaceae and with both pathogenic and non-pathogenic Neisseriaceae. In this study, we have measured antibody levels against the Po I site in patients with bacteraemia in order to examine the immunogenicity of the Po I domain in humans. A MAb-based competition ELISA (cELISA) was used. Only 20% of healthy controls had detectable levels of anti-Po I antibodies in serum. Of patients bacteraemic with enterobacteria (n = 45), 11% and 58% showed elevated antibody levels compared to healthy controls with the first and second serum specimens, respectively, and 73% of these patients showed > or = 10% increase in the antibody levels. Of patients bacteraemic with N. meningitidis (n = 20), only 30% showed > or = 10% increase in the antibody levels when paired serum specimens were tested. Levels of competing antibodies were similar in the cELISA with N. meningitidis (B: 15: P1, 7, 16) OM coat or E. coli O55 OM coat. The results demonstrated that the highly conserved porin protein domain Po I expressed immunogenicity in humans when present in bacteria which caused bacteraemia. This finding represents a challenge in further investigations on the immunobiological role of the cross-reacting antibodies.

Immunobiology of purified recombinant outer membrane porin protein I of Neisseria gonorrhoeae

Gonococcal porins (Por) from strains FA19 (Por-1, serogroup A), MS11 (Por-2, serogroup B) and FA6434 (Por-5, a hybrid porin containing epitopes from both serogroups), were expressed in Escherichia coli and purified under non-denaturing conditions. Porins were inserted into liposomes, and they were bound by monoclonal antibodies which bind native Por and intact gonococci, but not denatured Por. All three recombinant porins (rPor) were highly immunogenic in rabbits without additional adjuvant. The rPor antisera were specific for Por by Western blotting and whole-cell radioimmunoprecipitation and were broadly cross-reactive within serogroups. Post-immune, but not pre-immune, sera bound to intact gonococci, induced deposition of complement components C3 and C9 onto gonococcal membranes and increased association with and activation of human neutrophils. Gonococci were not killed in bactericidal assays, and there was no phagocytic killing with gonococci opsonized with recombinant antisera. Lack of killing in bactericidal assays was not caused by the presence of blocking antibodies to the outer-membrane protein Rmp.

Naturally occurring PIA/PIB hybrids of Neisseria gonorrhoeae

The major outer membrane protein of Neisseria gonorrhoeae, Por, functions as a porin and is thought to occur as one gene with two alleles. The immunologically distinct epitopes of the two subclasses, IA and IB, have allowed the development of serotyping schemes. Clinical isolates of N. gonorrhoeae are believed to express only a single type of Por, either IA or IB. We have encountered two clusters of isolates that react with antibodies to both IA and IB Por. Isolates within the clusters are indistinguishable by the phenotypic characteristics tested. In addition, the amplification of the por gene in representative isolates showed that the por gene of the hybrids gave similar restriction digest patterns within but not between the clusters.

The major anaerobically induced outer membrane protein of Neisseria gonorrhoeae, Pan 1, is a lipoprotein

Pan 1 is an acidic outer membrane protein of Neisseria gonorrhoeae that is expressed only when gonococci are grown anaerobically. On silver-stained sodium dodecyl sulfate-polyacrylamide gels, Pan 1 migrates as an intense but diffuse 54-kDa protein. The deduced amino acid sequence of Pan 1 from the aniA (anaerobically induced protein) open reading frame reveals a lipoprotein consensus sequence, Ala-Leu-Ala-Ala-Cys, and a processed molecular mass of 39 kDa. Furthermore, there is strong homology at the N terminus and C terminus of Pan 1 to the termini of the gonococcal outer membrane lipoproteins Lip and Laz. [3H]palmitic acid labeling of gonococci grown under oxygen-limited conditions demonstrated specific incorporation of label into Pan 1, suggesting further that Pan 1 is a lipoprotein.

Gonorrhoea: signs, symptoms and serogroups

Over 19 weeks, 104 male patients attending a genitourinary medicine clinic with gonococcal urethritis were asked to complete a questionnaire detailing symptoms. Sixty-seven questionnaires were duly completed. The examining nurse documented signs. Ninety-one isolates of Neisseria gonorrhoeae were serogrouped and auxotyped, 55 of these were from patients who had completed a questionnaire. Patients presented earlier if they had a past history of gonorrhoea (p = 0.02). The serogroup of N. gonorrhoeae did not influence the amount of discharge, the presence of meatal inflammation, dysuria or penile tip irritation or the delay in presentation after appearance of discharge. Auxotype AHU was not associated with asymptomatic gonorrhoea.

Fate of the major outer membrane protein P.IA in early and late events of gonococcal infection of epithelial cells

We investigated the fate of the major outer membrane protein of Neisseria gonorrhoeae, P.IA, during gonococcal infection of Chang conjunctiva epithelial cells by using immunoelectron microscopy. Probing of P.IA epitopes with mono- and polyclonal antibodies revealed variable, fixation-dependent P.IA epitope exposure in the gonococci used as an inoculum in the infection experiments. Detection of invariable exposed P.IA epitopes in cryosections of infected epithelial cells with a polyclonal antiserum revealed unaltered P.IA exposure on the bacterial membranes during early attachment of the bacteria to the eukaryotic cells. Upon entry of the bacteria into the host cells, however, labelling was extended to membraneous structures that intercalated between the bacteria and the host cell surface, and, occasionally, to the host cell plasma membrane. The latter observation is consistent with the suggested active role of P.I. in the uptake process (as shown in 1985 by E.C. Gotschlich). Once inside the epithelial cells, both morphologically intact and disintegrating bacteria could be distinguished. The disintegration of the bacteria was accompanied by a loss of P.IA immunoreactivity.

Bacterial entry and intracellular processing of Neisseria gonorrhoeae in epithelial cells: immunomorphological evidence for alterations in the major outer membrane protein P.IB

The fate of the major outer membrane protein of the gonococcus, P.IB, during the adherence, entry, and intracellular processing of the bacteria in infected epithelial cells was investigated using post-embedding immunoelectron microscopy. Various domains of the P.IB molecule were probed at different stages in the infection. These studies revealed that P.IB epitope exposure remained unaltered during the initial attachment of the bacteria to the host cells. In contrast, upon secondary attachment of the bacteria to the eukaryotic cells, apparent zones of adhesion were formed between the gonococci and the host cell membrane, which were characterized by loss of a defined P.IB epitope. These zones of adhesion with the altered P.IB immunoreactivity continued to exist and increased in number during cellular penetration, suggesting that they were essential to bacterial invasion into the eukaryotic cells. After bacterial entry, two classes of gonococci could be recognized; morphologically intact, P.IB-positive bacteria and disintegrated organisms that showed a change in, and, in a later stage, a complete loss of P.IB immunoreactivity. The intracellular alterations in the P.IB antigen could be prevented by treatment of the host cells with the lysosomotropic agent chloroquine. These observations point to a mechanism by which a subpopulation of intracellular gonococci can escape the epithelial cell defense by preventing or resisting exposure to host cell proteolytic activity.

Topology of outer membrane porins in pathogenic Neisseria spp

In Escherichia coli, membrane-spanning amphipathic beta-sheet structures are characteristic of many outer membrane proteins. By applying the principles that have been recognized for them to the four classes of neisserial porins, we have constructed a model for the topology of the porins within the outer membrane. This model predicts eight surface-exposed loops, both in the meningococcal class 1 and 2 proteins and in the gonococcal PIA and PIB proteins. The transmembrane sequences are highly conserved among these porins and are able to form an amphipathic beta-sheet structure. The surface-exposed hydrophilic loops show extensive variation in both length and sequence. Experimental evidence in support of this model has been obtained by using antisera against synthetic peptides which correspond to surface-exposed loops in class 1 and 2 proteins. Thus, binding to the cell surface was observed with antibodies against loops 1, 4, and 5 of class 1 and loops 1 and 5 of class 2. In class 1, these loops are the longest ones and show the highest sequence diversity among strains of different subtypes. Mapping of epitopes recognized by monoclonal antibodies with bactericidal activity has also provided strong support for the model. The epitopes are located in loops 1 and 4 of class 1 protein, loop 5 of PIB, and loop 6 of PIA. A nonbactericidal antibody that binds only weakly to whole cells was shown to recognize loop 3 of PIB. These results suggest that the longest loops are immunodominant, provide the binding sites for bactericidal antibodies, and display the greatest variation among different strains.

Comparison of the class 1 outer membrane proteins of eight serological reference strains of Neisseria meningitidis

Primers suitable for the amplification of the gene encoding the class 1 outer membrane protein of Neisseria meningitidis by the polymerase chain reaction (PCR) were designed from published DNA sequences and used to study the gene in eight meningococcal strains of different serogroup, serotype and subtype. At high annealing stringency one product, shown to correspond to the class 1 protein gene, was amplified from each strain. For three strains an additional smaller product, provisionally identified as the gene encoding the class 3 outer membrane protein, was amplified at lower annealing stringencies. Nucleotide sequence analysis of the PCR products corresponding to the class 1 proteins established the differences in the primary structure of the proteins between each of the subtypes and other outer-membrane proteins from Neisseria spp. These differences impose constraints on possible structural models of these proteins. Most amino acid sequence variation occurred in two domains of between 8 and 17 amino acids; there was an additional region which varied mainly between classes of outer membrane protein and there were nine conserved regions. Using appropriate primers it was possible to distinguish between class 1 outer membrane protein genes from strains of different subtypes by the PCR.

Distribution of a protein antigenically related to the major anaerobically induced gonococcal outer membrane protein among other Neisseria species

The Pan 1 protein of Neisseria gonorrhoeae is a novel 54-kDa outer membrane protein expressed only when gonococci are grown in the absence of oxygen. It is a major antigen recognized by sera from patients with gonococcal infection. We raised mouse monospecific polyclonal antiserum to gel-purified Pan 1 from gonococcal strain F62. The antiserum was broadly cross-reactive among gonococcal strains; all strains tested reacted in immunoblot analysis proportionate to the amount of Pan 1 visible in silver-stained sodium dodecyl sulfate (SDS)-polyacrylamide gels. In immunoblot experiments, N. lactamica and N. cinerea reacted very strongly to the anti-Pan 1 antiserum, whereas N. sicca, N. flava, and N. mucosa did not react at all. The other commensals tested, N. subflava and N. perflava, exhibited only a minor reaction. These results correlated with the apparent amount of Pan 1 seen on SDS-polyacrylamide gels of outer membranes. SDS-polyacrylamide gel analysis of six meningococcal strains revealed no visible anaerobically induced outer membrane proteins, and the subsequent immunoblots showed only slight or no reaction to the anti-Pan 1 antibody. In the four meningococcal strains that did react slightly with the antiserum, a Pan 1-like protein was seen only in anaerobically grown cells. Thus, meningococci did not express Pan 1 at levels comparable to that found in gonococci; however, when Pan 1 was expressed in meningococcal strains, it was oxygen regulated. This is the first example of a protein found in the gonococcal outer membrane that, under identical growth conditions, is not expressed at similar levels in the meningococcus.