Effect of mutations in the human immunoglobulin A1 (IgA1) hinge on its susceptibility to cleavage by diverse bacterial IgA1 proteases

Components of the human immunoglobulin A1 (IgA1) hinge governing sensitivity to cleavage by bacterial IgA1 proteases were investigated. Recombinant antibodies with distinct hinge mutations were constructed from a hybrid comprised of human IgA2 bearing half of the human IgA1 hinge region. This hybrid antibody and all the mutant antibodies derived from it were resistant to cleavage by the IgA1 proteases from Streptococcus oralis and Streptococcus mitis biovar 1 strains but were cleaved to various degrees by those of Streptococcus pneumoniae, some Streptococcus sanguis strains, and the type 1 and 2 IgA1 proteases of Haemophilus influenzae, Neisseria meningitidis, and Neisseria gonorrhoeae. Remarkably, those proteases that cleave a Pro-Ser peptide bond in the wild-type IgA1 hinge were able to cleave mutant antibodies lacking a Pro-Ser peptide bond in the hinge, and those that cleave a Pro-Thr peptide bond in the wild-type IgA1 hinge were able to cleave mutant antibodies devoid of a Pro-Thr peptide bond in the hinge. Thus, the enzymes can cleave alternatives to their preferred postproline peptide bond when such a bond is unavailable. Peptide sequence analysis of a representative antibody digestion product confirmed this conclusion. The presence of a cleavable peptide bond near the CH2 end of the hinge appeared to result in greater cleavage than if the scissile bond was at the CH1 end of the hinge. Proline-to-serine substitution at residue 230 in a hinge containing potentially cleavable Pro-Ser and Pro-Thr peptide bonds increased the resistance of the antibody to cleavage by many IgA1 proteases.

Analysis of the Piv recombinase-related gene family of Neisseria gonorrhoeae

Neisseria gonorrhoeae (the gonococcus) is an obligate human pathogen and the causative agent of the disease gonorrhea. The gonococcal pilus undergoes antigenic variation through high-frequency recombination events between unexpressed pilS silent copies and the pilin expression locus pilE. The machinery involved in pilin antigenic variation identified to date is composed primarily of genes involved in homologous recombination. However, a number of characteristics of antigenic variation suggest that one or more recombinases, in addition to the homologous recombination machinery, may be involved in mediating sequence changes at pilE. Previous work has identified several genes in the gonococcus with significant identity to the pilin inversion gene (piv) from Moraxella species and transposases of the IS110 family of insertion elements. These genes were candidates for a recombinase system involved in pilin antigenic variation. We have named these genes irg for invertase-related gene family. In this work, we characterize these genes and demonstrate that the irg genes do not complement for Moraxella lacunata Piv invertase or IS492 MooV transposase activities. Moreover, by inactivation of all eight gene copies and overexpression of one gene copy, we conclusively show that these recombinases are not involved in gonococcal pilin variation, DNA transformation, or DNA repair. We propose that the irg genes encode transposases for two different IS110-related elements given the names ISNgo2 and ISNgo3. ISNgo2 is located at multiple loci on the chromosome of N. gonorrhoeae, and ISNgo3 is found in single and duplicate copies in the N. gonorrhoeae and Neisseria meningitidis genomes, respectively.

Molecular analysis of oriT and MobA protein in the 7.4 kb mobilizable beta-lactamase plasmid pSJ7.4 from Neisseria gonorrhoeae

The mobilization region of the 7.4 kb beta-lactamase plasmid pSJ7.4 from Neisseria gonorrhoeae was characterized. The 3.2 kb HindIII-BamHI fragment of pSJ7.4 was mobilized between Escherichia coli strains by conjugative plasmid RK2. Selected restriction enzyme-generated deletions of this fragment were subcloned in pACYC177 to obtain constructs that were suitable for analysis of the mobilization region. Mating experiments showed that a highly conserved 1.9 kb DNA region within coordinates 4096-5997 is required for mobilization of pSJ7.4. This region contains two genes encoding the mobilization protein MobA, another protein, MobC, putatively involved in mobilization from some hosts, and an intergenic oriT. The 168 bp intergenic sequence also contains the promoters for mobA and mobC in an arrangement that suggests divergent transcription and autoregulation from oriT. The 56 kDa MobA was expressed in E. coli as a (6x)His-Tag fusion protein. Purified MobA specifically induced plasmid relaxation by nicking at the oriT. MobA is exceptional because the N-terminal region alone can mobilize pSJ7.4, albeit at a lower frequency than the full-length protein, even in the absence of MobC. The carboxyl terminal region of MobA did not share homology with other mobilization proteins, but may be involved in promoting efficient transfer of pSJ7.4.

Rapid detection of gyrA and parC mutations in fluoroquinolone-resistant Neisseria gonorrhoeae by denaturing high-performance liquid chromatography

The detection of DNA sequence variation is fundamental to the identification of the genomic basis of phenotypic variability. Denaturing high-performance liquid chromatography (DHPLC) is a novel technique that is used to detect mutations in human DNA. This is the first report that this technique is used as a tool to detect mutations in genes encoding fluoroquinolone resistance in Neisseria gonorrhoeae. Eighty-one strains of N. gonorrhoeae were used in this study. Genomic DNA from each strain was subjected to PCR amplification of 225 bp in gyrA and 166 bp in parC spanning the fluoroquinolone-resistance determining regions (QRDRs). After we performed DNA sequencing of these amplicons and identification of mutations in the QRDRs, DHPLC was undertaken to investigate whether its results correlate the distinctive chromatogram with their DNA mutations pattern. The profilings detected by DHPLC completely corresponded to the results of the DNA sequencing in mutation patters in gyrA and parC genes. They resulted in the following amino acid substitutions: Ser-91Phe, Asp-95Gly, and Asp-95Asn in gyrA; and Gly-85Asp, Asp-86Asn, Ser-87Arg, and Ser-88Pro in parC, respectively. These mutations existed alone or as combinations, and we identified five mutations patterns in gyrA and six in parC including wild-type. These mutations and their patterns could be rapidly and reproducibly identified from the PCR products using DHPLC, producing specific peak patterns that correlate with genotypes. This novel detection system facilitates the detection of resistance alleles, providing a rapid (5 min per sample), economic (96 sample per run), and reliable technique for characterizing fluoroquinolone resistance in N. gonorrhoeae.

Mutation of a single lytic transglycosylase causes aberrant septation and inhibits cell separation of Neisseria gonorrhoeae

The function of lytic peptidoglycan transglycosylases is poorly understood. Single lytic transglycosylase mutants of Escherichia coli have no growth phenotype. By contrast, mutation of Neisseria gonorrhoeae ltgC inhibited cell separation without affecting peptidoglycan monomer production. Thus, LtgC has a dedicated function in gonococcal cell division.

The N terminus of MinD contains determinants which affect its dynamic localization and enzymatic activity

MinD is involved in regulating the proper placement of the cytokinetic machinery in some bacteria, including Neisseria gonorrhoeae and Escherichia coli. Stimulation of the ATPase activity of MinD by MinE has been proposed to induce dynamic, pole-to-pole oscillations of MinD in E. coli. Here, we investigated the effects of deleting or mutating conserved residues within the N terminus of N. gonorrhoeae MinD (MinD(Ng)) on protein dynamism, localization, and interactions with MinD(Ng) and with MinE(Ng). Deletions or mutations were generated in the first five residues of MinD(Ng), and mutant proteins were evaluated by several functional assays. Truncation or mutation of N-terminal residues disrupted MinD(Ng) interactions with itself and with MinE. Although the majority of green fluorescent protein (GFP)-MinD(Ng) mutants could still oscillate from pole to pole in E. coli, the GFP-MinD(Ng) oscillation cycles were significantly faster and were accompanied by increased cytoplasmic localization. Interestingly, in vitro ATPase assays indicated that MinD(Ng) proteins lacking the first three residues or with an I5E substitution possessed higher MinE(Ng)-independent ATPase activities than the wild-type protein. These results indicate that determinants found within the extreme N terminus of MinD(Ng) are implicated in regulating the enzymatic activity and dynamic localization of the protein.

[Activity of enzymes of the tricarboxylic acid cycle in Neisseria gonorrhoeae strains resistant and sensitive to antibiotics]

The activity of enzymes of the tricarboxylic acid cycle and some enzymes which catalyze the reactions connected with the reactions cycle of Neisseria gonorrhoeae strains which contain plasmids with various spectrum and level of sensitivity to antibiotics has been studied. The decrease of activity of the basic enzymes of the cycle and intensification of anapleurotic reactions and reactions of constructive metabolism connected with the tricarboxylic acid cycle in antibiotic-resistant containing plasmids strains has been found.

A Neisseria gonorrhoeae catalase mutant is more sensitive to hydrogen peroxide and paraquat, an inducer of toxic oxygen radicals

Catalase is hypothesized to be critical in the protection of Neisseria gonorrhoeae from H2O2 produced during aerobic respiration and by phagocytes during infection. Here we cloned the catalase (kat) gene of gonococcal strain FA1090 and constructed a genetically defined N. gonorrhoeae kat mutant to assess the role of catalase in defense against oxidative stress. The gonococcal kat gene conferred increased H2O2 resistance to a catalase-deficient Escherichia coli strain. Mutation of the kat gene in strain FA1090 via an in-frame deletion resulted in increased sensitivity to H2O2 and paraquat, an inducer of toxic oxygen radicals. Expression of catalase in trans from a shuttle vector restored catalase activity and paraquat resistance to the kat mutant, but not resistance to H2O2. The inability to fully complement the mutant was perhaps due to a modification in the catalase, as evidenced by altered mobility of the recombinant catalase on activity gels when expressed from the shuttle vector in N. gonorrhoeae. Additionally, we showed a 262 base pair region upstream of the kat gene is required for expression in E. coli and a putative fumarate-nitrate regulator (FNR) binding site is located in this region.

Antimicrobial resistance of Neisseria gonorrhoeae in Japan, 1993–2002: continuous increasing of ciprofloxacin-resistant isolates

Susceptibility testing was conducted on 1357 isolates of Neisseria gonorrhoeae isolated from 1993 through 2002 in Japan to assess the antimicrobial resistance. Selected isolates were characterised by auxotype and analysis was done for mutations within the quinolone resistance-determining region (QRDR) in the gyrA and parC genes, which confer fluoroquinolone resistance to the organism. Isolates with ciprofloxacin resistance increased significantly from 6.6% (1993-1994) to 73.5% (2002). The proportion of plasmid-mediated penicillin-resistant isolates (PPNG) decreased significantly from 7.9% (1993-1994) to 0.9% (2002). The percentage of chromosomal-mediated resistance to penicillin decreased from 27.4% in 2000 to 12.0% in 2001 but increased to 28.9% in 2002. The proportion of isolates with any type of resistance to tetracycline decreased from 24.7% in 2000 to 13.9% in 2001 and then increased to 22.3% in 2002. The proportion of prototrophic isolates significantly decreased from 84.4% in 1992-1993 to 7.7% in 2001, while that of the proline-requiring isolates significantly increased from 4.4% in 1992-1993 and 80.8% in 1998. The proline-requiring isolates were less susceptible to ciprofloxacin than the prototrophic or arginine-requiring isolates. Of 87 isolates resistant to ciprofloxacin, 2 (2.3%) contained five amino acid substitutions within the GyrA and ParC proteins, 76 (87.4%) contained three or four amino acid substitutions and 9 (10.3%) contained one or two amino acid substitutions.

DNA methyltransferases from Neisseria meningitidis and Neisseria gonorrhoeae FA1090 associated with mismatch nicking endonucleases

The genes encoding the DNA methyltransferases M.NmeDI and M.NmeAI from Neisseria meningitidis associated with the genes encoding putative Vsr endonucleases were overexpressed in Escherichia coli. The enzymes were purified to apparent homogeneity on Ni-NTA agarose columns, yielding proteins of 49+/-1 kDa and 39.6+/-1 kDa, respectively, under denaturing conditions. M.NmeDI recognizes the degenerate sequence 5'-RCCGGB-3'. It methylates the first 5' cytosine residue on both strands within the core sequence CCGG. The enzyme shows higher affinity with the hemimethylated degenerate sequence than with the unmethylated degenerate sequence. Comparison of the amino acid sequence of the target-recognizing domain of M.NmeDI with the closest neighbours recognizing the sequence 5'-RCCGGY-3' showed the presence of the homologous domain and an additional domain that may be responsible for recognizing the degenerate sequence. M.NmeAI recognizes the sequence 5'-CCGG-3' and methylates the second 5' cytosine residue on both DNA strands. In Neisseria gonorrhoeae strain FA1090 the homologues of these ORFs are truncated due to a variety of mutations.

Gonorrhoea in young heterosexuals attending urban STD clinics in Britain: a cross-sectional survey

Young people in the UK bear the brunt of sexually transmitted infections, in particular of gonorrhoea. We aimed to assess whether young people with gonorrhoea (under 21 years) attending sexual health clinics differed from older individuals with gonorrhoea in their behavioural and clinical characteristics and management outcomes. The results of this cross-sectional study suggest that young people were more likely to be female (66.2% vs 34.1%), have concurrent infection with Chlamydia trachomatis (55.4% vs 30.2%) and a history of recent gonococcal infection (81.3% vs 35.5%) if they ever had gonorrhoea. Young women were more likely to experience treatment delay and not to attend for follow-up than older women. Resistance to ciprofloxacin was high in both age groups but the prevalence of penicillinase-producing Neisseria gonorrhoeae was higher in older patients (11.5% vs 1.3%). Different management protocols for young and older patients with gonorrhoea may need to be considered.

High Occurrence of Simultaneous Mutations in Target Enzymes and MtrRCDE Efflux System in Quinolone-Resistant Neisseria gonorrhoeae

BACKGROUND

Emergence of multidrug-resistant Neisseria gonorrhoeae resulting from new genetic mutations is a serious threat to controlling gonorrhea.

GOAL

To determine 1) antimicrobial susceptibilities and the corresponding genetic mutations and 2) the role of MtrRCDE efflux system in gonococcal resistance to fluoroquinolones.

STUDY DESIGN

Antimicrobial susceptibility testing and sequence analysis of gyrA, parC, and mtrR loci of 131 N. gonorrhoeae isolates from Japan.

RESULTS

The proportion of N. gonorrhoeae strains resistant and intermediate-resistant to antimicrobials was 25.2% and 48.9% for ciprofloxacin, 25.2% and 30.5% for ofloxacin, 12.2% and 53.4% for penicillin; and 17.6% and 51.1% for tetracycline, respectively. Strains were categorized into 22 mutation profiles, with GyrA-S91F/ParC-D86N/MtrR-G45D being the most predominant profile. The frequency of mutation in gyrA, parC, mtrR, and the mtrR promoter was 71%, 47.3%, 77.1%, and 23.7%, respectively. Seventy-one percent of strains carried mutations in both gyrA and mtrR.

CONCLUSION

This study reports simultaneous mutations in fluoroquinolone target enzymes and the MtrRCDE efflux system as a fluoroquinolone-resistant mechanism in N. gonorrhoeae.

Characterization of the -1,2-N-acetylglucosaminyltransferase of Neisseria gonorrhoeae, a key control point in lipooligosaccharride biosynthesis

The biosynthesis of the lipooligosaccharide (LOS) in Neisseria meningitidis has a control point that regulates the extension of the alpha-chain on heptose (I) of the LOS. The gene that encodes the protein responsible for this control had been identified elsewhere, but the enzyme encoded by the gene was not characterized. We have now shown that this same control mechanism operates in the related species, Neisseria gonorrhoeae, using a gene knockout and subsequent characterization of the LOS species produced. We also cloned and expressed the enzyme from both of these pathogens. Using a synthetic acceptor substrate, we have shown unequivocally that the enzyme is an alpha-1,2-N-acetylglucosaminyltransferase. Experiments with both the core oligosaccharide and the synthetic acceptors suggests that the addition of the alpha-1,2-N-acetylglucosamine moiety on the heptose (II) residue precedes the addition of the ethanolamine phosphate at the O3 position on this heptose (II), and that in the absence of the alpha-1,2-N-acetylglucosamine moiety leads to the addition of an extra ethanolamine phosphate on the heptose (II) residue. Our data do not support the hypothesis that ethanolamine phosphate at O3 of heptose (II) is added and is then required for the addition of the N-acetylglucosamine at O2 by the LgtK enzyme. This enzyme represents a control point in the biosynthesis of the LOS of this pathogen and is a potential target for therapeutic intervention.

Neutralization of enteric coronaviruses with Escherichia coli cells expressing single-chain Fv-autotransporter fusions

We report here that fusions of single-chain antibodies (scFvs) to the autotransporter beta domain of the IgA protease of Neisseria gonorrhoeae are instrumental in locating virus-neutralizing activity on the cell surface of Escherichia coli. E. coli cells displaying scFvs against the transmissible gastroenteritis coronavirus on their surface blocked in vivo the access of the infectious agent to cultured epithelial cells. This result raises prospects for antiviral strategies aimed at hindering the entry into target cells by bacteria that naturally colonize the same intestinal niches.

[A molecular-epidemiologic study on TEM-1 genes of Neisseria gonorrhoeae in Wuxi area]

OBJECTIVE

In order to study the epidemiology of TEM-1 genes of Neisseria gonorrhoeae (Ng) in Wuxi area.

METHODS

In the light from foreign literature that positive Ng strains of beta-lactamase contain plasmid sequences of TEM-1 genes, heminested PCR for TME-1 genes of Ng detection was self-designed. Ng of 195 strains were detected, that were isolated in Wuxi area from Jan to the Oct, 2002.

RESULTS

There were 138 TEM-1 genes positive in 195 isolated strains with a positive rate of 70.8%. There was one case of heminested PCR product of TEM-1 genes which showed the homogeneity was 99% in Wuxi area, when comparing with pFA7 sequences of positive Ng plasmid of beta-lactase from register GenBank.

CONCLUSION

Data showed that the Ng strains with TEM-1 genes were the prevalent ones in Wuxi area.

Frequency of alterations in the GyrA subunit of DNA gyrase and the ParC subunit of topoisomerase IV in 19 clinical isolates of Neisseria gonorrhoeae in Tokyo in 2002

The frequency of alterations in the GyrA subunit of DNA gyrase and the ParC subunit of topoisomerase IV in 19 clinical isolates of Neisseria gonorrhoeae obtained in Tokyo in 2002 was studied. The frequencies of GyrA and ParC mutations in these 19 isolates were 100% (19 of 19) and 84.2% (16 of 19), respectively, and these results were 1.48-fold (100%/67.6%) and 3.58-fold (84.2%/23.5%) higher, respectively, than the frequencies reported in 1998 in 68 isolates obtained in Fukuoka during the period from 1992 to 1996. Isolates with increasing numbers of mutations were more resistant not only to levofloxacin but also to other antibiotics. The 50% and 90% minimum inhibitory concentrations (MICs) to levofloxacin during the period from 1995 to 1996 were 0.063 and 1 micro g/ml, and they increased to 4 and 8 micro g/ml, respectively, in the present study. All 19 cases of gonoccocal urethritis in the present study were cured with a single intramuscular injection of 2 g spectinomycin.

Overexpression and enzymatic characterization of Neisseria gonorrhoeae penicillin-binding protein 4

The penicillin-binding proteins (PBPs) are ubiquitous bacterial enzymes involved in cell wall biosynthesis, and are the targets of the beta-lactam antibiotics. The low molecular mass Neisseria gonorrhoeae PBP 4 (NG PBP 4) is the fourth PBP revealed in the gonococcal genome. NG PBP 4 was cloned, overexpressed, purified, and characterized for beta-lactam binding, DD-carboxypeptidase activity, acyl-donor substrate specificity, transpeptidase activity, inhibition by a number of active site directed reagents, and pH profile. NG PBP 4 was efficiently acylated by penicillin (30,000 m-1.s-1). Against a set of five alpha- and epsilon-substituted l-Lys-D-Ala-D-Ala substrates, NG PBP 4 exhibited wide variation in specificity with a preference for N epsilon-acylated substrates, suggesting a possible preference for crosslinked pentapeptide substrates in the cell wall. Substrates with an N epsilon-Cbz group demonstrated pronounced substrate inhibition. NG PBP 4 showed 30-fold higher activity against the depsipeptide Lac-ester substrate than against the analogous peptide substrate, an indication that k2 (acylation) is rate determining for carboxypeptidase activity. No transpeptidase activity was apparent in a model transpeptidase reaction. Among a number of active site-directed agents, N-chlorosuccinimide, elastinal, iodoacetamide, iodoacetic acid, and phenylglyoxal gave substantial inhibition, and methyl boronic acid gave modest inhibition. The pH profile for activity against Ac2-l-Lys-D-Ala-d-Ala (kcat/Km) was bell-shaped, with pKa values at 6.9 and 10.1. Comparison of the enzymatic properties of NG PBP 4 with other DD-carboxypeptidases highlights both similarities and differences within these enzymes, and suggests the possibility of common mechanistic roles for the two highly conserved active site lysines in Class A and C low molecular mass PBPs.

Evaluation of four methods for detecting the beta-lactamase activity in Neisseria gonorrhoeae isolated in Cuba

Four methods (chromogenic, acidimetric, inhibition, and iodometric) for demonstration of the beta-lactamase production by 70 isolates of Neisseria gonorrhoeae, were evaluated in Cuba. There was 100% correlation between all beta-lactamase methods and the standardized penicillin dilution susceptibility test for penicillinase-non-producing N. gonorrhoeae. For penicillinase-producing N. gonorrhoeae strains, there was a perfect correlation between the chromogenic method and penicillin susceptibility testing, but one and two strains failed to give a positive result for beta-lactamase with the inhibition/acidimetric and the iodometric methods, respectively. There was a high concordance between the chromogenic method, considered as gold standard and the rest of penicillinase tests evaluated: Kappa Index (KI) = 0.98 for inhibition/acidimetric methods and KI = 0.97 for the iodometric method. The four methods evaluated were accurate, reproducible, easily readable, economical, and ease to use for screening primary isolates of N. gonorrhoeae in Cuba. We recommended the use of the inhibition method, when testing the penicillinase activity in gonococcal isolates in provincial and municipal reference laboratories.

Neisseria gonorrhoeaePenicillin-Binding Protein 3 Exhibits Exceptionally High Carboxypeptidase and β-Lactam Binding Activities†,‡

A soluble form of penicillin-binding protein 3 (PBP 3) from Neisseria gonorrhoeae was expressed and purified from Escherichia coli and characterized for its interaction with beta-lactam antibiotics, its catalytic properties with peptide and peptidoglycan substrates, and its role in cell viability and morphology. PBP 3 had an unusually high k(2)/K' value relative to other PBPs for acylation with penicillin (7.7 x 10(5) M(-1) s(-1)) at pH 8.5 at 25 degrees C and hydrolyzed bound antibiotic very slowly (k(3) < 4.6 x 10(-5) s(-1), t(1/2) > 230 min). PBP 3 also demonstrated exceptionally high carboxypeptidase activity with a k(cat) of 580 s(-1) and a k(cat)/K(m) of 1.8 x 10(5) M(-1) s(-1) with the substrate N(alpha)-Boc-N(epsilon)-Cbz-L-Lys-D-Ala-D-Ala. This is the highest k(cat) value yet reported for a PBP or other serine peptidases. Activity against a approximately D-Ala-D-Lac peptide substrate was approximately 2-fold lower than against the analogous approximately D-Ala-D-Ala peptide substrate, indicating that deacylation is rate determining for both amide and ester hydrolysis. The pH dependence profiles of both carboxypeptidase activity and beta-lactam acylation were bell-shaped with maximal activity at pH 8.0-8.5. PBP 3 displayed weak transpeptidase activity in a model transpeptidase reaction but was active as an endopeptidase, cleaving dimeric peptide cross-links. Deletion of PBP 3 alone had little effect on viability, growth rate, and morphology of N. gonorrhoeae, although deletion of both PBP 3 and PBP 4, the other low-molecular-mass PBP in N. gonorrhoeae, resulted in a decreased growth rate and marked morphological abnormalities.

Gonococcal phospholipase d modulates the expression and function of complement receptor 3 in primary cervical epithelial cells

CR3-mediated endocytosis is a primary mechanism by which Neisseria gonorrhoeae elicits membrane ruffling and cellular invasion of the cervical epithelia. Our data indicate that, upon infection of cervical epithelia, N. gonorrhoeae specifically releases proteins, including a phospholipase D (PLD) homolog, which facilitate membrane ruffling. To elucidate the function of gonococcal PLD in infection of the cervical epithelia, we constructed an N. gonorrhoeae PLD mutant. By comparative association and/or invasion assays, we demonstrated that PLD mutant gonococci are impaired in their ability to adhere to and to invade primary cervical cells. This defect can be rescued by the addition of supernatants obtained from wild-type-infected cell monolayers but not by exogenously added Streptomyces PLD. The decreased level of total cell association (i.e., adherence and invasion) observed for mutant gonococci is, in part, attributed to the inability of these bacteria to recruit CR3 to the cervical cell surface with extended infection. Using electron microscopy, we demonstrate that gonococcal PLD may be necessary to potentiate membrane ruffling and clustering of gonococci on the cervical cell surface. These data may be indicative of the inability of PLD mutant gonococci to recruit CR3 to the cervical cell surface. Alternatively, in the absence of gonococcal PLD, signal transduction events required for CR3 clustering may not be activated. Collectively, our data indicate that PLD augments CR3-mediated gonococcus invasion of and survival within cervical epithelia.

Mutation of a family 8 glycosyltransferase gene alters cell wall carbohydrate composition and causes a humidity-sensitive semi-sterile dwarf phenotype in Arabidopsis

The genome of Arabidopsis thaliana contains about 400 genes coding for glycosyltransferases, many of which are predicted to be involved in the synthesis and remodelling of cell wall components. We describe the isolation of a transposon-tagged mutant, parvus, which under low humidity conditions exhibits a severely dwarfed growth phenotype and failure of anther dehiscence resulting in semi-sterility. All aspects of the mutant phenotype were partially rescued by growth under high-humidity conditions, but not by the application of growth hormones or jasmonic acid. The mutation is caused by insertion of a maize Dissociation (Ds) element in a gene coding for a putative Golgi-localized glycosyltransferase belonging to family 8. Members of this family, originally identified on the basis of similarity to bacterial lipooligosaccharide glycosyltransferases, include enzymes known to be involved in the synthesis of bacterial and plant cell walls. Cell-wall carbohydrate analyses of the parvus mutant indicated reduced levels of rhamnogalacturonan I branching and alterations in the abundance of some xyloglucan linkages that may, however, be indirect consequences of the mutation.

A novel cytochrome c peroxidase from Neisseria gonorrhoeae: a lipoprotein from a Gram-negative bacterium

A cytochrome c peroxidase (CCP) produced by Neisseria gonorrhoeae has been shown to have novel characteristics by investigating its location, expression and role in Neisseria gonorrhoeae and by expression in Escherichia coli. Analysis of the N-terminus of CCP indicated that it is a lipoprotein with a signal peptide for cleavage by signal peptidase II. Expression of the gonococcal CCP in E. coli revealed that it is first synthesized as a pro-apo-cytochrome that is translocated across the cytoplasmic membrane. The signal peptide is cleaved and haem is attached in the periplasm. The gonococcal CCP was associated with the membrane of both E. coli and N. gonorrhoeae. The expression of a MalE-CCP fusion protein has allowed characterization of CCP in vitro. Evidence is presented that CCP protects gonococci from hydrogen peroxide, presumably in the periplasmic compartment of the cell. The expression of CCP is dependent on the transcription factor FNR, but is repressed by nitrite, indicating that it could be most important in the stationary-phase response. These data support the hypothesis that the gonococcal lipoprotein CCP is anchored to the membrane in the periplasm, where it might be responsible for the reduction of hydrogen peroxide. Other putative CCP lipoproteins have been identified, representing a new subclass of bacterial CCP proteins.

Characterization and expression of adjacent proline iminopeptidase and aspartase genes from Eikenella corrodens

Two adjacent genes involved in nitrogen metabolism from Eikenella corrodens, with a potential role in pathogenesis, were studied. Proline iminopeptidase (Pip) activity, which may be essential for energy production and protection against host immune mechanisms, is exhibited by E. corrodens. Analysis of Pip-expressing clones revealed an ORF of 939 bases with a predicted amino acid sequence identity of 67% to the Pip of Neisseria gonorrhoea. 200 bp downstream from pip, an ORF of 1395 bases, encoding a protein with 87% identity to a putative aspartase from the Neisseria meningitidis genome sequence, was identified. Enzymatic function was confirmed with a complemented Escherichia coli aspartase deficient mutant. The E. corrodens aspartase was found to be 77% identical to the Haemophilus influenzae aspartase sequence, which was originally identified on the basis of its ability to bind plasminogen. However, the E. corrodens aspartase had no such activity. Southern hybridization indicated both genes to be single copy and conserved within the genomes of a diverse panel of E. corrodens isolates from health and disease.

A Sco homologue plays a role in defence against oxidative stress in pathogenic Neisseria

Sco proteins are found in mitochondria and in a variety of oxidase positive bacteria. Although Sco is required for the formation of the Cu(A) centre in a cytochrome oxidase of the aa(3) type, it was observed that oxidases with a Cu(A) centre are not present in many bacteria that contain a Sco homologue. Two bacteria of this type are the pathogens Neisseria meningitidis and Neisseria gonorrhoeae. The sco genes of N. gonorrhoeae strain 1291 and N. meningitidis strain MC58 were cloned, inactivated by inserting a kanamycin resistance cassette and used to make knockout mutants by allelic exchange. Both N. gonorrhoeae and N. meningitidis sco mutants were highly sensitive to oxidative killing by paraquat, indicating that Sco is involved in protection against oxidative stress in these bacteria.