Purification and antigenic relatedness of proteins II of Neisseria gonorrhoeae

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.

Gonococcal transferrin-binding protein 1 is required for transferrin utilization and is homologous to TonB-dependent outer membrane receptors

The pathogenic Neisseria species are capable of utilizing transferrin as their sole source of iron. A neisserial transferrin receptor has been identified and its characteristics defined; however, the biochemical identities of proteins which are required for transferrin receptor function have not yet been determined. We identified two iron-repressible transferrin-binding proteins in Neisseria gonorrhoeae, TBP1 and TBP2. Two approaches were taken to clone genes required for gonococcal transferrin receptor function. First, polyclonal antiserum raised against TBP1 was used to identify clones expressing TBP1 epitopes. Second, a wild-type gene copy was cloned that repaired the defect in a transferrin receptor function (trf) mutant. The clones obtained by these two approaches were shown to overlap by DNA sequencing. Transposon mutagenesis of both clones and recombination of mutagenized fragments into the gonococcal chromosome generated mutants that showed reduced binding of transferrin to whole cells and that were incapable of growth on transferrin. No TBP1 was produced in these mutants, but TBP2 expression was normal. The DNA sequence of the gene encoding gonococcal TBP1 (tbpA) predicted a protein sequence homologous to the Escherichia coli and Pseudomonas putida TonB-dependent outer membrane receptors. Thus, both the function and the predicted protein sequence of TBP1 were consistent with this protein serving as a transferrin receptor.

Interactions of Neisseria gonorrhoeae with human neutrophils: studies with purified PII (Opa) outer membrane proteins and synthetic Opa peptides

We investigated the role of gonococcal outer membrane protein PII (also called Opa protein) in nonopsonic adherence to human neutrophils. Gonococcal outer membranes, purified Opa in detergent (Opa), purified Opa in liposomes (Opa+ lips), and peptides composing the second hypervariable (HV2) region of OpaB (strain FA1090) in liposomes (pepHV2 lips) were tested for their abilities to inhibit subsequent gonococcal adherence to human neutrophils. Outer membranes from gonococci possessing adherent Opa, liposomes containing adherent Opa, purified adherent Opa, and two of three liposome preparations (pepHV2 lips) containing peptides from the HV2 region of an adherent Opa inhibited subsequent adherence to neutrophils of homologous Opa+ gonococci. On the other hand, outer membranes from Opa- gonococci, outer membranes containing a nonadherent Opa (OpaA from strain FA1090), purified OpaA, and OpaA lips had little or no inhibitory effect. Outer membranes containing adherent Opas, purified adherent Opas, and liposomes containing such Opas all bound to neutrophils, whereas preparations containing OpaA or no Opa protein did not. The results indicate that (i) Opa proteins can bind to neutrophils in a partially purified or purified form and (ii) the HV2 region of Opa appears to at least partially mediate Opa's biological role.

In situ expression and localization of Neisseria gonorrhoeae opacity proteins in infected epithelial cells: apparent role of Opa proteins in cellular invasion

During natural infection, gonococcal opacity proteins (Opa) undergo rapid phase variation, but how this phenomenon contributes to the virulence of the bacteria is not well understood. In the present immunomorphological study we examined the actual Opa status of individual gonococci during various stages of gonococcal infection of Chang epithelial cells, by probing ultrathin sections of infected specimens with Opa-specific monoclonal antibodies. Our results demonstrate a heterogeneous Opa expression during the initial interaction of the bacteria, but an almost 100% expression of one of the probed Opas during their secondary attachment and entry into the host cells, suggesting a role for distinct Opas in cellular penetration. The association between Opa expression, tight attachment, and bacterial invasion into the host cells could be confirmed with isogenic variants that expressed different Opa proteins. Once inside the epithelial cells, both morphologically intact, Opa positive and morphologically disintegrated, Opa negative bacteria were observed. The loss of Opa immunoreactivity in intracellular gonococci could not be related to the presence of a particular Opa protein, but could be mimicked by incubating the organisms with extracts of sonicated uninfected epithelial cells, suggesting that it was caused by host cell proteolytic activity. Taken together, our data suggest that Opa phase transitions confer a functional adaptation of the bacteria enabling host cell penetration.

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.

Monoclonal antibodies to outer membrane protein PII block interactions of Neisseria gonorrhoeae with human neutrophils

Nonopsonic binding of gonococci to human neutrophils appears to be mediated by a family of heat-modifiable outer membrane proteins termed protein IIs (PIIs). We studied the ability of a wide variety of antigonococcal monoclonal antibodies (MAbs) to inhibit the interactions of nonpiliated PII+ gonococci with human neutrophils by measuring gonococcal adherence to neutrophils and subsequent luminol-enhanced neutrophil chemiluminescence. From one set of 95 MAbs reacting with whole gonococci, only two, 7VA2 and 7B9, inhibited the ability of gonococci to induce neutrophil chemiluminescence. 7VA2 and 7B9 both reacted only with PII. MAb 53C4, from a smaller set of anti-PII MAbs, inhibited adherence to neutrophils of PII variants that bound 53C4, but not of PII variants that did not. It also inhibited gonococcus-induced neutrophil chemiluminescence. Using a whole-cell binding assay and Western blotting (immunoblotting), we showed that MAb 53C4 bound to one PII (PII4) of strain F62 and to two PIIs (PIIb and PIId) of strain FA1090. The present studies confirm and extend the role of PII in gonococcal adherence to and stimulation of human neutrophils and show intrastrain conservation of PII epitopes. The results indicate that PII is the only outer membrane component involved in adherence of nonpiliated gonococci to human neutrophils.

Expression of gonococcal protein II in Escherichia coli by translational fusion

A protein II (P.II) gene from Neisseria gonorrhoeae was cloned in Escherichia coli and characterized by DNA sequence analysis. As with other reported P.II sequences, this gene contains an ATG initiation codon which is out of frame with respect to the remainder of the P.II amino acid sequence. A translational fusion was constructed in E. coli which linked the P.II sequence to the signal peptide of beta-lactamase. This P.II fusion differs from the gonococcal protein only in the first seven residues at the N terminus. In E. coli, the P.II fusion product exhibits properties analogous to those of P.II in N. gonorrhoeae. The P.II fusion product is a major component of the E. coli outer membrane and it is exposed on the cell surface. The P.II fusion protein also exhibits the heat-modifiable phenotype of gonococcal P.II.

Expression of outer membrane protein II by gonococci in experimental gonorrhea

Gonorrheal urethritis was induced in three males by intraurethral instillation of predominantly pilus+ protein II- gonococci. Virtually all gonococci reisolated from the infected men exhibited protein II+ phenotype. The reisolated gonococci expressed five distinct outer membrane protein II species. Protein IIc+ organisms predominated in urines of all three subjects, but variants expressing this particular protein II were rarely spawned in vitro by input organisms. Protein IIc+ gonococci appeared early in one man's infection; they were joined later by variants that displayed eight other protein II phenotypes, including protein II-. These results show that input protein II- gonococci are supplanted by protein IIc+ variants during incipient gonorrheal urethritis. As infection progresses, a broader variety of protein II+ variants appears.

Purification and characterization of eight class 5 outer membrane protein variants from a clone of Neisseria meningitidis serogroup A

Methods published for the purification of P.II proteins from Neisseria gonorrhoea have been modified to allow the purification of class 5 proteins from Neisseria meningitidis serogroup A bacteria. The five class 5 protein electrophoretic variants detected within an epidemic in the Gambia (a, b, c, d, and e) and three other variants (f, g, and h) found within other isolates of the same clone in West Africa have been purified with yields of 6-28 mg. The NH2-terminal amino acid sequence for variant c differs from those of the other class 5 proteins, whereas the latter are very similar to the sequence predicted for two class 5 proteins from DNA analyses of serogroup C meningococci and determined for 8 P.II proteins from gonococci. Numerous other regulatory, chemical, and serological differences were found between the c protein and the other class 5 proteins such that we recommend that the class 5 proteins be subdivided into two subclasses. mAbs have been isolated that distinguish between these two protein subclasses and Western blotting with these antibodies enabled us to conclude that both protein subclasses were found in bacteria isolated from different epidemics and pandemics of the last 50 yr.

Immunoelectron microscopic localization of outer membrane proteins II on the surface of Neisseria gonorrhoeae

To determine the ultrastructural distribution and immunological accessibility of proteins II (P.IIs) on the surfaces of whole gonococci, anti-P.II gold probes were developed and used in electron microscopic studies of viable P.II-expressing variants of Neisseria gonorrhoeae FA1090. Anti-P.II probes clearly marked the surfaces of organisms and their associated outer membrane blebs. The surface-exposed portion of P.II is antigenically variable. With the use of two different sizes of gold probes, it was demonstrated that individual gonococcal cells can express more than one antigenic type of P.II simultaneously.

Antigenic and structural differences among six proteins II expressed by a single strain of Neisseria gonorrhoeae

Gonococci express a family of related outer membrane proteins designated protein II (P.II), which undergo both phase and antigenic variation. Six P.II proteins have been identified in strain FA1090. We developed monoclonal antibodies specific for each P.II protein. Using these antibodies as probes, we purified the six different P.II proteins of this strain. Despite the relatedness of the proteins, we could not purify all of them by a single purification scheme. Four P.II proteins were purified by chromatofocusing, and the remaining two proteins were purified by hydrophobic interaction chromatography on phenyl-Sepharose. The N-terminal amino acid sequence of the proteins showed a high degree of sequence conservation. However, there was variability at specific amino acid residues, giving each P.II protein a unique N-terminal amino acid sequence. Thus P.II proteins of one strain differ among themselves not only in antigenic determinants and primary structure, but also in other characteristics affecting their properties in different chromatographic systems.