Serosubtypes and PorA types of Neisseria meningitidis serogroup B isolated in Brazil during 1997--1998: overview and implications for vaccine development

Meningococcal disease caused by N. meningitidis serogroup B (MenB) has been endemic in Brazil since 1997. In this study, we determined the prevalence of serosubtypes of MenB isolated in 10 Brazilian states and the Federal District during 1997 and 1998 and investigated the extent of PorA VR sequence variation among the most prevalent serosubtypes to evaluate the possible use of an outer membrane vesicle (OMV)-, PorA-based vaccine to prevent meningococcal disease in Brazil. During this period, a total of 8,932 cases of meningococcal disease were reported. Only 42% (n = 3,751) of the reported cases were laboratory confirmed, and about 60% (n = 2,255) of those were identified as MenB. Among 1,297 MenB strains selected for this study, the most prevalent serosubtypes were P1.19,15 (66%), P1.7,1 (11%), and P1.7,16 (4%). PorA VR typing showed that 91% of the P1.19,15 strains analyzed had VR1 and VR2 sequences identical to those of the prototype strain. No sequence variation was detected among the 40 strains representing all isolated MenB P1.7,16 strains in the three southern states, where this serosubtype accounts for 75% of the serosubtypes identified. Similarly, all P1.7,1 strains were identified by PorA typing as P1.7-1,1. Although further improvements in the reporting of cases and collection of strains in Brazil are needed, our data suggest that a trivalent OMV-based vaccine prepared with PorA types P1.19,15, P1.7-1,1, and P1.7,16 may be appropriate to control serogroup B meningococcal disease in most of the Brazilian states.

A Mg-dependent ecto-ATPase in Leishmania amazonensis and its possible role in adenosine acquisition and virulence

The plasma membrane of cells contains enzymes whose active sites face the external medium rather than the cytoplasm. The activities of these enzymes, referred to as ectoenzymes, can be measured using living cells. In this work we describe the ability of living promastigotes of Leishmania amazonensis to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (5.39 +/- 0.71 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 30.75 +/- 2.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. The addition of MgCl(2) to extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. At 5 mM ATP, half-maximal stimulation of ATP hydrolysis was obtained with 1.21 mM MgCl(2). This stimulatory activity was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2) or SrCl(2). The apparent K(m) for Mg-ATP(2-) was 0.98 mM and free Mg(2+) did not increase the ecto-ATPase activity. In the pH range from 6.8 to 8.4, in which the cells were viable, the acid phosphatase activity decreased, while the Mg(2+)-dependent ATPase activity increased. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A(1), ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, 4,4'-diisothiocyanostylbene 2',2'-disulfonic acid as well as suramin, an antagonist of P(2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. A comparison between the Mg(2+)-dependent ATPase activity of virulent and avirulent promastigotes showed that avirulent promastigotes were less efficient than the virulent promastigotes in hydrolyzing ATP.

Genetic relationships among serogroup B: serotype 4 Neisseria meningitidis strains

We compared the results obtained by serotyping of PorB epitopes using an expanded panel of monoclonal antibodies (mAb) including mAb 7 and mAb 10, with results obtained by RFLP of rRNA genes (ribotyping). The purpose of this study was to assess the correlation between phenotypic- and genotypic- methods for typing N. meningitidis. The ribotypes obtained using ClaI or EcoRV endonucleases grouped the strains in seven and two different patterns, respectively. This additional characterization of PorB epitopes improved the correlation between these two methods of typing N. meningitidis.

p-Nitrophenylphosphatase activity catalyzed by plasma membrane (Ca(2+) + Mg(2+)ATPase: correlation with structural changes modulated by glycerol and Ca(2+)

The plasma membrane (Ca(2+) + Mg(2+))ATPase hydrolyzes pseudo-substrates such as p-nitrophenylphosphate. Except when calmodulin is present, Ca(2+) ions inhibit the p-nitrophenylphosphatase activity. In this report it is shown that, in the presence of glycerol, Ca(2+) strongly stimulates phosphatase activity in a dose-dependent manner. The glycerol- and Ca(2+)-induced increase in activity is correlated with modifications in the spectral center of mass (average emission wavenumber) of the intrinsic fluorescence of the enzyme. It is concluded that the synergistic effect of glycerol and Ca(2+) is related to opposite long-term hydration effects on the substrate binding domain and the Ca(2+) binding domain.

Effects of naturally occurring polyols and urea on mitochondrial F0F1ATPase

We show that urea inhibits the ATPase activity of MgATP submitochondrial particles (MgATP-SMP) with Ki = 0.7 M, probably as a result of direct interaction with the structure of F0F1-ATPase. Counteracting compounds (sorbitol, mannitol or inositol), despite slightly (10-20%) inhibiting the ATPase activity, also protect the F0F1-ATPase against denaturation by urea. However, this protection was only observed at low urea concentrations (less than 1.5 M), and in the presence of three polyols, the Ki for urea shift from 0.7 M to 1.2 M. Urea also increases the initial activation rate of latent MgATP-SMP in a dose-dependent-manner. However, when the particles (0.5 mg/ml) were preincubated in the presence of 1 M, 2 M or 3 M urea, a decrease in the activation level occurred after 1 h, 30 and 10 min, respectively. At high MgATP-SMP concentration (3 mg/ml) a decrease in activation was observed after 2 h, 1 h and 20 min, respectively. These data indicate that the effect of urea on the activation of MgATP-SMP depends on time, urea and protein concentrations. It was also observed that polyols suppress the activation of latent MgATP-SMP in a dose-dependent manner, and protect the particles against urea denaturation during activation. We suppose that a decrease in membrane mobility promoted by interactions of polyols with phospholipids around the F0F1-ATPase may also increase the compactation of protein structure, explaining the inhibition of natural inhibitor protein of ATPase (IF1) release and the activation of the enzyme.

Proposed standardization of Neisseria meningitidis PorA variable-region typing nomenclature

Neisseria meningitidis isolates are conventionally classified by serosubtyping, which characterizes the reactivities of the PorA outer membrane protein variable-region (VR) epitopes with monoclonal antibodies (MAbs). A newer method (PorA VR typing) uses predicted amino acid sequences derived from DNA sequence analysis. The resulting classification schemes are not standardized, offering conflicting and sometimes irreconcilable data from the two methods. In this paper, we propose a standardization of the PorA VR typing nomenclature that incorporates serologic information from traditional PorA serosubtyping with molecular data from predicted VR sequences. We performed a comprehensive literature and database search, generating a collection of strains and DNA sequences that reflects the diversity within PorA that exists to date. We have arranged this information in a comprehensive logical model that includes both serosubtype and PorA VR type assignments. Our data demonstrate that the current panel of serosubtype-defining MAbs underestimates PorA VR variability by at least 50%. Our proposal for VR typing is informative because amino acid sequence and serologic information, when serosubtype-defining MAbs are available, can be deduced simultaneously from the PorA VR designation. This scheme will be useful in future classification and applied epidemiologic studies of N. meningitidis, being a systematic way of selecting PorA vaccine candidates and analyzing vaccine coverage and failure.

Correlation between serological and sequencing analyses of the PorB outer membrane protein in the Neisseria meningitidis serotyping system

The current serological typing scheme for Neisseria meningitidis is not comprehensive; a proportion of isolates are not serotypeable. DNA sequence analysis and predicted amino acid sequences were used to characterize the structures of variable-region (VR) epitopes on N. meningitidis PorB proteins (PorB VR typing). Twenty-six porB gene sequences were obtained from GenBank and aligned with 41 new sequences. Primary amino acid structures predicted from those genes were grouped into 30 VR families of related variants that displayed at least 60% similarity. We correlated VR families with monoclonal antibody (MAb) reactivities, establishing a relationship between VR families and epitope locations for 15 serotype-defining MAbs. The current panel of serotype-defining MAbs underestimates by at least 50% the PorB VR variability because reagents for several major VR families are lacking or because a number of VR variants within some families are not recognized by serotype-defining MAbs. These difficulties, also reported for serosubtyping based on the PorA protein, are shown as inconsistent results between serological and sequence analyses, leading to inaccurate strain identification and incomplete epidemiological data. The information from this study enabled the expansion of the panel of MAbs currently available for serotyping, by including MAbs of previously undetermined specificities. Use of the expanded serotype panel enabled us to improve the sensitivity of serotyping by resolving a number of formerly nonserotypeable strains. In most cases, this information can be used to predict the VR family placement of unknown PorB proteins without sequencing the entire porB gene. PorB VR typing complements serotyping, and a combination of both techniques may be used for full characterization of meningococcal strains. The present work represents the most complete and integrated data set of PorB VR sequences and MAb reactivities of serogroup B and C meningococci produced to date.

Carbohydrate protection of enzyme structure and function against guanidinium chloride treatment depends on the nature of carbohydrate and enzyme

Baker's yeast cells accumulate osmolytes as a response to several stress conditions such as high-temperature and low-temperature shifts, dehydration, or osmotic stress. One of the major osmolytes that accumulates is trehalose, which plays an essential role affecting the survival of yeast at the time of stress. In this report, we show that trehalose efficiently protects the function and the structure of two yeast cytosolic enzymes against chemical denaturation by guanidinium chloride. Other sugars tested also protected yeast pyrophosphatase and glucose-6-phosphate dehydrogenase structure against guanidinium chloride effects, but were not as efficient at protecting enzyme activity. The thermostable pyrophosphatase from Bacillus stearothermophilus was also protected by several sugars against the chaotropic properties of guanidinium chloride, but was only protected by trehalose against functional inactivation. The function of the membrane-embedded H+-ATPase from yeast could not be protected by any of the tested sugars, although all of the sugars protected its structure from guanidinium-chloride-induced unfolding. The results presented in this study suggest that several sugars are able to prevent protein unfolding induced by a chaotropic compound. However, prevention of functional inactivation depends on the nature of the sugar. Trehalose was the most efficient, being able to protect many cytosolic enzymes against guanidinium chloride. The efficiency of protection also depended on the nature of the protein tested. This might explain why trehalose is one of the osmolytes accumulated in yeast and also why it is not the only osmolyte to accumulate.

Ultrastructural and biochemical analysis of the relationship of Crithidia deanei with its endosymbiont

Some protozoa of the Trypanosomatidae family harbor in their cytoplasm bacterial endosymbionts that provide essential nutrients to and induce morphological alterations in the protozoa. In the present study, a close association between endosymbionts and glycosomes, a peroxisome-like organelle where most of the enzymes of the glycolytic pathway are compartmentalized, was identified by conventional transmission electron microscopy in Crithidia deanei. Such an association was further supported by the cytochemical localization of catalase in the glycosome and also confirmed by 3-D reconstruction of the protozoan. The enzymes cytochrome oxidase and succinate dehydrogenase were detected by ultrastructural cytochemistry. A positive reaction was observed in the protozoan mitochondrion but not in the endosymbiont envelope. Enzymatic assays for succinate cytochrome c reductase reinforced these results, as a low enzymatic activity was detected in an endosymbiont-enriched fraction, while high activity was observed in a purified protozoan mitochondrion fraction. We also demonstrated that a purified symbiont fraction was able to hydrolyze ATP. This activity was Mg+2 dependent, since it was highly stimulated by the presence of physiological concentrations of this ion. Taken together, these observations suggest that no electron transporting system is active in the symbionts of Crithidia deanei and that they might obtain energetic molecules derivated from the protozoan glycosomes.

Antibody response after immunization of Brazilian children with serogroup C meningococcal polysaccharide noncovalently complexed with outer membrane proteins

We have studied the antibody response of Brazilian vaccinees to C meningococcal polysaccharide (C-PS) after one or two doses of a vaccine composed of C-PS, outer membrane proteins of B meningococci and aluminum hydroxide. Total IgG, IgG1 and IgG2 as well as bactericidal activity mediated by complement were measured in serum samples from children 3 to 83 months of age (post-vaccination IgG, IgG1 and IgG2 levels of 2.4 to 13.4 micrograms/ml; less than 18 to 67.8 U/ml and less than 18 to 106.8 U/ml, respectively) and from individuals 10 to 14 years of age (post-vaccination IgG, IgG1 and IgG2 levels of 14.6 micrograms/ml, 23.7 U/ml and 112.0 U/ml, respectively). The antibody response, measured as IgG levels, was age-dependent. Although high antibody levels were demonstrable by enzyme-linked immunosorbent assay (ELISA), bactericidal activity was not demonstrable (less than 1:4) in serum from children aged less than 24 months. A significant bactericidal activity was detected in serum of children older than 49 months of age and in individuals 10 to 14 years of age. A predominance of IgG2 was observed in post-vaccination serum samples from children belonging to those two age groups. The antibody concentration sufficient to confer protection as well as the possible causes of the poor correlation observed between ELISA and bactericidal activity results are discussed.