Mapping the functional interaction of Sco1 and Cox2 in cytochrome oxidase biogenesis

Sco1 is implicated in the copper metallation of the Cu(A) site in Cox2 of cytochrome oxidase. The structure of Sco1 in the metallated and apo-conformers revealed structural dynamics primarily in an exposed region designated loop 8. The structural dynamics of loop 8 in Sco1 suggests it may be an interface for interactions with Cox17, the Cu(I) donor and/or Cox2. A series of conserved residues in the sequence motif (217)KKYRVYF(223) on the leading edge of this loop are shown presently to be important for yeast Sco1 function. Cells harboring Y219D, R220D, V221D, and Y222D mutant Sco1 proteins failed to restore respiratory growth or cytochrome oxidase activity in sco1Delta cells. The mutant proteins are stably expressed and are competent to bind Cu(I) and Cu(II) normally. Specific Cu(I) transfer from Cox17 to the mutant apo-Sco1 proteins proceeds normally. In contrast, using two in vivo assays that permit monitoring of the transient Sco1-Cox2 interaction, the mutant Sco1 molecules appear compromised in a function with Cox2. The mutants failed to suppress the respiratory defect of cox17-1 cells unlike wild-type SCO1. In addition, the mutants failed to suppress the hydrogen peroxide sensitivity of sco1Delta cells. These studies implicate different surfaces on Sco1 for interaction or function with Cox17 and Cox2.     

Evidence for a pro-oxidant intermediate in the assembly of cytochrome oxidase

The hydrogen peroxide sensitivity of cells lacking two proteins, Sco1 and Cox11, important in the assembly of cytochrome c oxidase (CcO), is shown to arise from the transient accumulation of a pro-oxidant heme A-Cox1 stalled intermediate. The peroxide sensitivity of these cells is abrogated by a reduction in either Cox1 expression or heme A formation but exacerbated by either enhanced Cox1 expression or heme A production arising from overexpression of COX15. Sco1 and Cox11 are implicated in the formation of the Cu(A) and Cu(B) sites of CcO, respectively. The respective wild-type genes suppress the peroxide sensitivities of sco1Delta and cox11Delta cells, but no cross-complementation is seen with noncognate genes. Copper-binding mutant alleles of Sco1 and Cox11 that are nonfunctional in promoting the assembly of CcO are functional in suppressing the peroxide sensitivity of their respective null mutants. Likewise, human Sco1 that is nonfunctional in yeast CcO assembly is able to suppress the peroxide sensitivity of yeast sco1Delta cells. Thus, a disconnect exists between the respiratory capacity of cells and hydrogen peroxide sensitivity. Hydrogen peroxide sensitivity of sco1Delta and cox11Delta cells is abrogated by overexpression of a novel mitochondrial ATPase Afg1 that promotes the degradation of CcO mitochondrially encoded subunits. Studies on the hydrogen peroxide sensitivity in CcO assembly mutants reveal new aspects of the CcO assembly process.     

HmbR outer membrane receptors of pathogenic Neisseria spp.: iron-regulated, hemoglobin-binding proteins with a high level of primary structure conservation.

We have recently cloned and characterized the hemoglobin receptor gene from Neisseria meningitidis serogroup C. N. meningitidis cells expressing HmbR protein were able to bind biotinylated hemoglobin, and the binding was specifically inhibited by unlabeled hemoglobin and not heme. The HmbR-mediated hemoglobin binding activity of N. meningitidis cells was shown to be iron regulated. The presence of hemoglobin but not heme in the growth medium stimulated HmbR-mediated hemoglobin binding activity. The efficiency of utilization of different hemoglobins by the HmbR-expressing N. meningitidis cells was shown to be species specific; human hemoglobin was the best source of iron, followed by horse, rat, turkey, dog, mouse, and sheep hemoglobins, The phenotypic characterization of HmbR mutants of some clinical strains of N. meningitidis suggested the existence of two unrelated hemoglobin receptors. The HmbR-unrelated hemoglobin receptor was shown to be identical to Hpu, the hemoglobin-haptoglobin receptor of N. meningitidis. The Hpu-dependent hemoglobin utilization system was not able to distinguish between different sources of hemoglobin; all animal hemoglobins were utilized equally well. HmbR-like genes are also present in N. meningitidis serogroups A and B, Neisseria gonorrhoeae MS11 and FA19, Neisseria perflava, and Neisseria polysaccharea. The hemoglobin receptor genes from N. meningitidis serogroups A and B and N. gonorrhoeae MS11 were cloned, and their nucleotide sequences were determined. The nucleotide sequence identity ranged between 86.5% (for N. meningitidis serogroup B hmbR and MS11 hmbR) and 93.4% (for N. meningitidis serogroup B hmbR and N. meningitidis serogroup C hmbR). The deduced amino acid sequences of these neisserial hemoglobin receptors were also highly related, with overall 84.7% conserved amino acid residues. A stop codon was found in the hmbR gene of N. gonorrhoeae MS11. This strain was still able to use hemoglobin and hemoglobin-haptoglobin complexes as iron sources, indicating that some gonococci may express only the HmbR-independent hemoglobin utilization system.     

PilC of Neisseria meningitidis is involved in class II pilus formation and restores pilus assembly, natural transformation competence and adherence to epithelial cells in PilC-deficient gonococci

Type 4 pili produced by the pathogenic Neisseria species constitute primary determinants for the adherence to host tissues. In addition to the major pilin subunit (PilE), neisserial pili contain the variable PilC proteins represented by two variant gene copies in most pathogenic Neisseria isolates. Based upon structural differences in the conserved regions of PilE, two pilus classes can be distinguished in Neisseria meningitidis . For class I pili found in both Neisseria gonorrhoeae and N. meningitidis , PilC proteins have been implicated in pilus assembly, natural transformation competence and adherence to epithelial cells. In this study, we used primers specific for the pilC2 gene of N. gonorrhoeae strain MS11 to amplify, by the polymerase chain reaction, and clone a homologous pilC gene from N. meningitidis strain A1493 which produces class II pili. This gene was sequenced and the deduced amino acid sequence showed 75.4% and 73.8% identity with the gonococcal PilC1 and PilC2, respectively. These values match the identity value of 74.1% calculated for the two N. gonorrhoeae MS11 PilC proteins, indicating a horizontal relationship between the N. gonorrhoeae and N. meningitidis pilC genes. We provide evidence that PilC functions in meningococcal class II pilus assembly and adherence. Furthermore, expression of the cloned N. meningitidis pilC gene in a gonococcal pilC1,2 mutant restores pilus assembly, adherence to ME-180 epithelial cells, and transformation competence to the wild-type level. Thus, PilC proteins exhibit indistinguishable functions in the context of class I and class II pili.     

Ecological separation and genetic isolation of Neisseria gonorrhoeae and Neisseria meningitidis

BACKGROUND: Classifying bacteria into species is problematic. Most microbiologists consider species to be groups of isolates that share some arbitrary degree of relatedness of biochemical or molecular (such as DNA sequence) features and that, ideally, are clearly delineated from all other groups of isolates. The main problem in applying to bacteria a biological concept of species based on the ability or inability of their genes to recombine, is that recombination appears to be rare in bacteria in nature, as indicated by the strong linkage disequilibrium between alleles found in most bacterial populations. However, there are some naturally transformable bacteria in which assortative recombination appears to be so frequent that alleles are in, or close to, linkage equilibrium. For these recombining populations a biological concept of species might be applicable. RESULTS: Populations of Neisseria gonorrhoeae and Neisseria meningitidis from Spain were analysed by multilocus enzyme electrophoresis. The data indicate that assortative recombination occurs frequently within populations, but not between populations. Similarly, the sequences of two house-keeping genes show no evidence of intragenic recombination between N. gonorrhoeae and N. meningitidis. CONCLUSIONS: N. gonorrhoeae and N. meningitidis represent extremely closely related 'sexual' populations that appear to be genetically isolated in nature, and thus conform to the biological concept of species. The extreme uniformity of N. gonorrhoeae house-keeping genes suggests that this species may have arisen recently as a clone of N. meningitidis that could colonize the genital tract. Ecological isolation - of populations that can colonize the genital tract from those that can colonize the nasopharynx - may have been an important component in speciation, leading to a lower frequency of recombination between species than within species.     

A study by high-resolution two-dimensional polyacrylamide gel electrophoresis of relationships between Neisseria gonorrhoeae and other bacteria

High-resolution two-dimensional polyacrylamide gel electrophoresis was used to analyse the soluble proteins from seven strains of Neisseria gonorrhoeae, six strains of Neisseria meningitidis and one or two strains of twelve other species. Approximately 200 individual polypeptides could be visualized as Coomassie Blue stained spots on an electrophoretogram of N. gonorrhoeae and similar numbers were found for the other bacteria. Each species of bacterium had a distinctly different pattern of spots which could be recognized. Quantitative comparisons of 48 selected spots derived from one strain of N. gonorrhoeae with those of five other strains of gonococcus, three strains of N. meningitidis and one of Branhamella catarrhalis, showed relationships in agreement with their current taxonomic classification but with a higher level of discrimination than that of previously used methods. It was also possible to distinguish the individual gonococcal strains. It is suggested that the method could be useful for bacterial classification and identification.     

Genome analysis and strain comparison of correia repeats and correia repeat-enclosed elements in pathogenic Neisseria

Whole genome sequences of Neisseria meningitidis strains Z2491 and MC58 and Neisseria gonorrhoeae FA1090 were analyzed for Correia repeats (CR) and CR-enclosed elements (CREE). A total of 533, 516, and 256 copies of CR and 270, 261, and 102 copies of CREE were found in these three genomes, respectively. The lengths of CREE range from 28 to 348 bp, and the lengths of multicopy CREE appear mainly in the ranges of 154 to 156 bp and 105 to 107 bp. The distribution of CREE lengths is similar between the two N. meningitidis genomes, with a greater number of 154- to 156-bp CREE (163 and 152 copies in N. meningitidis strain Z2491 and N. meningitidis strain MC58, respectively) than 105- to 107-bp CREE (72 and 77 copies). In the N. gonorrhoeae strain FA1090 genome there are relatively more 105- to 107-bp CREE (51 copies) than 154- to 156-bp CREE (36 copies). The genomic distribution of 107-bp CREE also shows similarity between the two N. meningitidis strains (15 copies share the same loci) and differences between N. meningitidis strains and N. gonorrhoeae FA1090 (only one copy is located in the same locus). Detailed sequence analysis showed that both the terminal inverted repeats and the core regions of CREE are composed of distinct basic sequence blocks. Direct TA dinucleotide repeats exist at the termini of all CREE. A survey of DNA sequence upstream of the sialyltransferase gene, lst, in several Neisseria isolates showed that 5 N. meningitidis strains contain a 107-bp CREE in this region but 25 N. gonorrhoeae strains show an exact absence of a 105-bp sequence block (i.e., the 107-bp CREE without a 5' TA dinucleotide) in the same region. Whole-genome sequence analysis confirmed that this 105-bp indel exists in many homologous 107-bp CREE loci. Thus, we postulate that all CREE are made of target TA with indels of various lengths. Analysis of 107-bp CREE revealed that they exist predominantly in intergenic regions and are often near virulence, metabolic, and transporter genes. The abundance of CREE in Neisseria genomes suggests that they may have played a role in genome organization, function, and evolution. Their differential distribution in different pathogenic Neisseria strains may contribute to the distinct behaviors of each Neisseria species.     

Epithelial cell responses induced upon adherence of pathogenic Neisseria

Neisseria meningitidis and Neisseria gonorrhoeae colonize human mucosal surfaces and cause sepsis/meningitis and gonorrhoea respectively. The first step in the infection process is pilus-mediated adhesion of the bacteria to epithelial cells, followed by host cell invasion. Adhesion of pathogenic Neisseria elicits multiple responses in host cells, including cellular signalling events, cytokine production and modulation of the eukaryotic cell surface. We used microarrays to assess the respective involvement of 375 human cytokine and adhesion related genes during adhesion of piliated and non-piliated N. gonorrhoeae, and piliated encapsulated N. meningitidis to the epithelial cell line ME-180. We identified 29 differentially regulated genes not previously reported to respond to neisserial infections, many of which encode membrane proteins. Selected genes were further analysed by semiquantitative RT-PCR, and protein expression was examined by flow cytometry. We found that N. gonorrhoeae elicited a different inflammatory response than N. meningitidis and we also demonstrated that early adhesion events are responsible for the induction of specific genes. Our data create a new platform for elucidating the interaction between pathogenic Neisseria and target cells.     

Structural characterization of outer membrane components of the type IV pili system in pathogenic Neisseria

Structures of the type IV pili secretin complexes from Neisseria gonorrhoeae and Neisseria meningitidis, embedded in outer membranes were investigated by transmission electron microscopy. Single particle averaging revealed additional domains not observed previously. Secretin complexes of N. gonorrhoeae showed a double ring structure with a 14-15-fold symmetry in the central ring, and a 14-fold symmetry of the peripheral ring with 7 spikes protruding. In secretin complexes of N. meningitidis, the spikes were absent and the peripheral ring was partly or completely lacking. When present, it had a 19-fold symmetry. The structures of the complexes in several pil mutants were determined. Structures obtained from the pilC1/C2 adhesin and the pilW minor pilin deletion strains were similar to wild-type, whereas deletion of the homologue of N. meningitidis PilW resulted in the absence of secretin structures. Remarkably, the pilE pilin subunit and pilP lipoprotein deletion mutants showed a change in the symmetry of the peripheral ring from 14 to 19 and loss of spikes. The pilF ATPase mutant also lost the spikes, but maintained 14-fold symmetry. These results show that secretin complexes contain previously unidentified large and flexible extra domains with a probable role in stabilization or assembly of type IV pili.     

Deoxyribonucleic Acid Homologies Among Species of the Genus Neisseria

Eleven aerobic species of Neisseria, a Mima sp., and a Herellea sp. were tested for deoxyribonucleic acid (DNA) homology in direct hybridization experiments. DNA labeled with either (14)C or (32)P was prepared from five species of Neisseria. Unlabeled DNA from the various microorganisms was immobilized on membrane filters, which, after pretreatment, were incubated with labeled DNA (4,000 counts per min per filter) for 14 hr at 67 C. The measure of relatedness was expressed as the relative percentage of direct binding compared to that obtained with homologous DNA. All serological types of N. meningitidis, including the newly proposed types, were homologous to the standard strain of N. meningitidis with one possible exception, type Z. The genus Neisseria is heterogeneous in nature, forming at least three distinct groups: first, N. meningitidis and N. gonorrhoeae; second, N. perflava, N. subflava, N. sicca, N. flavescens, and N. flava; third, N. catarrhalis and N. caviae. Mima and Herellea species show no significant homology with the Neisseria.     

Conjugal transfer of beta-lactamase-producing plasmids of Neisseria gonorrhoeae to Neisseria meningitidis

Twenty clinical isolates of beta-lactamase-producing Neisseria gonorrhoeae from Japanese sources were studied to define their ability to serve as donors for their plasmids in conjugation with Neisseria meningitidis. These twenty strains of N. gonorrhoeae harbored the 4.5-megadalton (Mdal) beta-lactamase-producing plasmids and the 24.5-Mdal conjugative plasmids. We found that only three of twenty N. gonorrhoeae strains showed a detectable conjugation frequency (greater than 10(-5)) with N. meningitidis as the recipient although all strains were capable of mobilizing beta-lactamase-producing plasmids to N. gonorrhoeae and to Escherichia coli. The 4.5-Mdal beta-lactamase-producing plasmid was maintained in N. meningitidis, but the large 24.5-Mdal conjugative plasmid has not been found in N. meningitidis transconjugants.     

The lipopolysaccharide (R type) as a common antigen of Neisseria gonorrhoeae. II. Use of hen antiserum to gonococcal lipopolysaccharide in a rapid slide test for the identification of N. gonorrhoeae from primary isolates and secondary cultures.

An antiserum has been prepared in hens to R-type gonococcal lipopolysaccharide (LPS) and used in a simple slide-agglutination test for the identification of Neisseria gonorrhoeae. Anti-LPS serum agglutinated gonococcal cells representative of the four colony types of N. gonorrhoeae. Absorption of the antiserum with LPS removed the agglutinating activity. Secondary cultures (1120) were tested without observation of the colony type and all were agglutinated. No agglutination occurred with strains of Neisseria meningitidis, Neisseria lactamica, non-pathogenic Neisseria. Pseudomonas aeruginosa, Branhamella catarrhalis, or with species of lactobacilli and Acinetobacter. Cross-reactivity of the antiserum occurred with some streptococci. The anti-LPS serum was used to identify N. gonorrhoeae in primary isolates from the cervix, urethra, and pharynx. Of 251 gonococcal isolates tested, 249 were agglutinated by the antiserum, while all of the corresponding second cultures were agglutinated. The antiserum did not agglutinate N. meningitidis found in primary isolates from pharyngeal specimens. Anti-LPS hen serum should be useful for the rapid identification of N. gonorrhoeae in primary isolates or secondary cultures.     

The P174L mutation in human Sco1 severely compromises Cox17-dependent metallation but does not impair copper binding

Sco1 is a metallochaperone that is required for copper delivery to the Cu(A) site in the CoxII subunit of cytochrome c oxidase. The only known missense mutation in human Sco1, a P174L substitution in the copper-binding domain, is associated with a fatal neonatal hepatopathy; however, the molecular basis for dysfunction of the protein is unknown. Immortalized fibroblasts from a SCO1 patient show a severe deficiency in cytochrome c oxidase activity that was partially rescued by overexpression of P174L Sco1. The mutant protein retained the ability to bind Cu(I) and Cu(II) normally when expressed in bacteria, but Cox17-mediated copper transfer was severely compromised both in vitro and in a yeast cytoplasmic assay. The corresponding P153L substitution in yeast Sco1 was impaired in suppressing the phenotype of cells harboring the weakly functional C57Y allele of Cox17; however, it was functional in sco1delta yeast when the wild-type COX17 gene was present. Pulse-chase labeling of mitochondrial translation products in SCO1 patient fibroblasts showed no change in the rate of CoxII translation, but there was a specific and rapid turnover of CoxII protein in the chase. These data indicate that the P174L mutation attenuates a transient interaction with Cox17 that is necessary for copper transfer. They further suggest that defective Cox17-mediated copper metallation of Sco1, as well as the subsequent failure of Cu(A) site maturation, is the basis for the inefficient assembly of the cytochrome c oxidase complex in SCO1 patients.     

Pathogenic neisseriae can use hemoglobin, transferrin, and lactoferrin independently of the tonB locus

Redundant TonB systems which function in iron transport from TonB-dependent ligands have recently been identified in several gram-negative bacteria. We demonstrate here that in addition to the previously described tonB locus, an alternative system exists for the utilization of iron from hemoglobin, transferrin, or lactoferrin in Neisseria meningitidis and Neisseria gonorrhoeae. Following incubation on media containing hemoglobin, N. meningitidis IR3436 (tonB exbB exbD deletion mutant) and N. gonorrhoeae PD3401 (tonB insertional mutant) give rise to colonies which can grow with hemoglobin. Transfer of Hb(+) variants (PD3437 or PD3402) to media containing hemoglobin, transferrin, and/or lactoferrin as sole iron sources resulted in growth comparable to that observed for the wild-type strains. Transformation of N. meningitidis IR3436 or N. gonorrhoeae PD3401 with chromosomal DNA from the Hb(+) variants yielded transformants capable of growth with hemoglobin. When we inactivated the TonB-dependent outer membrane hemoglobin receptors (HmbR or HpuB) in the Neisseria Hb(+) variants, these strains could not grow with hemoglobin; however, growth was observed with transferrin and/or lactoferrin. These results demonstrate that accumulation of iron from hemoglobin, transferrin, and lactoferrin in the pathogenic neisseriae can occur via a system that is independent of the previously described tonB locus.     

Pilin glycosylation in Neisseria meningitidis occurs by a similar pathway to wzy-dependent O-antigen biosynthesis in Escherichia coli

Pili (type IV fimbriae) of Neisseria meningitidis are glycosylated by the addition of O-linked sugars. Recent work has shown that PglF, a protein with homology to O-antigen 'flippases', is required for the biosynthesis of the pilin-linked glycan and suggests pilin glycosylation occurs in a manner analogous to the wzy-dependent addition of O-antigen to the core-LPS. O-Antigen ligases are crucial in this pathway for the transfer of undecraprenol-linked sugars to the LPS-core in Gram-negative bacteria. An O-antigen ligase homologue, pglL, was identified in N. meningitidis. PglL mutants showed no change in LPS phenotypes but did show loss of pilin glycosylation, confirming PglL is essential for pilin O-linked glycosylation in N. meningitidis.     

Genetic characterization of pilin glycosylation and phase variation in Neisseria meningitidis

Pili of Neisseria meningitidis are a key virulence factor, being the major adhesin of this capsulate organism and contributing to specificity for the human host. Pili are post-translationally modified by addition of either an O-linked trisaccharide, Gal (beta1-4) Gal (alpha1-3) 2,4-diacetamido-2,4,6-trideoxyhexose or an O-linked disaccharide Gal (alpha1,3) GlcNAc. The role of these structures in meningococcal pathogenesis has not been resolved. In previous studies we identified two separate genetic loci, pglA and pglBCD, involved in pilin glycosylation. Putative functions have been allocated to these genes; however, there are not enough genes to account for the complete biosynthesis of the described structures, suggesting additional genes remain to be identified. In addition, it is not known why some strains express the trisaccharide structure and some the disaccharide structure. In order to find additional genes involved in the biosynthesis of these structures, we used the recently published group A strain Z2491 and group B strain MC58 Neisseria meningitidis genomes and the unfinished Neisseria meningitidis group C strain FAM18 and Neisseria gonorrhoeae strain FA1090 genomes to identify novel genes involved in pilin glycosylation, based on homology to known oligosaccharide biosynthetic genes. We identified a new gene involved in pilin glycosylation designated pglE and examined four additional genes pglB/B2, pglF, pglG and pglH. A strain survey revealed that pglE and pglF were present in each strain examined. The pglG, pglH and pglB2 polymorphisms were not found in strain C311 musical sharp 3 but were present in a large number of clinical isolates. Insertional mutations were constructed in pglE and pglF in N. meningitidis strain C311 musical sharp 3, a strain with well-defined lipopolysaccharide (LPS) and pilin-linked glycan structures. Increased gel migration of the pilin subunit molecules of pglE and pglF mutants was observed by Western analysis, indicating truncation of the trisaccharide structure. Antisera specific for the C311 musical sharp 3 trisaccharide failed to react with pilin from these pglE and pglF mutants. GC-MS analysis of the sugar composition of the pglE mutant showed a reduction in galactose compared with C311 musical sharp 3 wild type. Analysis of amino acid sequence homologies has suggested specific roles for pglE and pglF in the biosynthesis of the trisaccharide structure. Further, we present evidence that pglE, which contains heptanucleotide repeats, is responsible for the phase variation between trisaccharide and disaccharide structures in strain C311 musical sharp 3 and other strains. We also present evidence that pglG, pglH and pglB2 are potentially phase variable.