Structure and Assembly of a Trans-Periplasmic Channel for Type IV Pili in Neisseria meningitidis

Type IV pili are polymeric fibers which protrude from the cell surface and play a critical role in adhesion and invasion by pathogenic bacteria. The secretion of pili across the periplasm and outer membrane is mediated by a specialized secretin protein, PilQ, but the way in which this large channel is formed is unknown. Using NMR, we derived the structures of the periplasmic domains from N. meningitidis PilQ: the N-terminus is shown to consist of two β-domains, which are unique to the type IV pilus-dependent secretins. The structure of the second β-domain revealed an eight-stranded β-sandwich structure which is a novel variant of the HSP20-like fold. The central part of PilQ consists of two α/β fold domains: the structure of the first of these is similar to domains from other secretins, but with an additional α-helix which links it to the second α/β domain. We also determined the structure of the entire PilQ dodecamer by cryoelectron microscopy: it forms a cage-like structure, enclosing a cavity which is approximately 55 Å in internal diameter at its largest extent. Specific regions were identified in the density map which corresponded to the individual PilQ domains: this allowed us to dock them into the cryoelectron microscopy density map, and hence reconstruct the entire PilQ assembly which spans the periplasm. We also show that the C-terminal domain from the lipoprotein PilP, which is essential for pilus assembly, binds specifically to the first α/β domain in PilQ and use NMR chemical shift mapping to generate a model for the PilP:PilQ complex. We conclude that passage of the pilus fiber requires disassembly of both the membrane-spanning and the β-domain regions in PilQ, and that PilP plays an important role in stabilising the PilQ assembly during secretion, through its anchorage in the inner membrane.     

Genetic Diversity and Levels of Expression of Factor H Binding Protein among Carriage Isolates of Neisseria meningitidis

The prevention of meningococcal disease may be improved by recombinant vaccines such as 4CMenB and rLP2086 that target the factor H binding protein (fHbp), an immunogenic surface component of Neisseria meningitidis present as one of three variants. Whether such vaccines decrease carriage of invasive isolates and thus induce herd immunity is unknown. We analyzed the genetic diversity and levels of expression of fHbp among 268 carriage strains and compare them to those of 467 invasive strains. fhbp gene sequencing showed higher proportions of variants 2 and 3 among carriage isolates (p<0.0001). Carriage isolates expressed lower levels of fHbp (p<0.01) but that remain high enough to predict targeting by antibodies against fHbp particularly in group B isolates belonging to the frequent hypervirulent clonal complexes in Europe and North America (cc32, cc41/44, cc269). This suggests that fHbp targeting meningococcal vaccines might reduce, at least in part, the acquisition of some hyperinvasive isolates.     

Use of a Molecular Decoy to Segregate Transport from Antigenicity in the FrpB Iron Transporter from Neisseria meningitidis

FrpB is an outer membrane transporter from Neisseria meningitidis, the causative agent of meningococcal meningitis. It is a member of the TonB-dependent transporter (TBDT) family and is responsible for iron uptake into the periplasm. FrpB is subject to a high degree of antigenic variation, principally through a region of hypervariable sequence exposed at the cell surface. From the crystal structures of two FrpB antigenic variants, we identify a bound ferric ion within the structure which induces structural changes on binding which are consistent with it being the transported substrate. Binding experiments, followed by elemental analysis, verified that FrpB binds Fe³⁺ with high affinity. EPR spectra of the bound Fe³⁺ ion confirmed that its chemical environment was consistent with that observed in the crystal structure. Fe³⁺ binding was reduced or abolished on mutation of the Fe³⁺-chelating residues. FrpB orthologs were identified in other Gram-negative bacteria which showed absolute conservation of the coordinating residues, suggesting the existence of a specific TBDT sub-family dedicated to the transport of Fe³⁺. The region of antigenic hypervariability lies in a separate, external sub-domain, whose structure is conserved in both the F3-3 and F5-1 variants, despite their sequence divergence. We conclude that the antigenic sub-domain has arisen separately as a result of immune selection pressure to distract the immune response from the primary transport function. This would enable FrpB to function as a transporter independently of antibody binding, by using the antigenic sub-domain as a ‘molecular decoy’ to distract immune surveillance.     

Prevalence and Phase Variable Expression Status of Two Autotransporters,NalP and MspA,in Carriage and Disease Isolates of Neisseria meningitidis

Neisseria meningitidis is a human nasopharyngeal commensal capable of causing life-threatening septicemia and meningitis. Many meningococcal surface structures, including the autotransporter proteins NalP and MspA, are subject to phase variation (PV) due to the presence of homopolymeric tracts within their coding sequences. The functions of MspA are unknown. NalP proteolytically cleaves several surface-located virulence factors including the 4CMenB antigen NhbA. Therefore, NalP is a phase-variable regulator of the meningococcal outer membrane and secretome whose expression may reduce isolate susceptibility to 4CMenB-induced immune responses. To improve our understanding of the contributions of MspA and NalP to meningococcal-host interactions, their distribution and phase-variable expression status was studied in epidemiologically relevant samples, including 127 carriage and 514 invasive isolates representative of multiple clonal complexes and serogroups. Prevalence estimates of >98% and >88% were obtained for mspA and nalP, respectively, with no significant differences in their frequencies in disease versus carriage isolates. 16% of serogroup B (MenB) invasive isolates, predominately from clonal complexes ST-269 and ST-461, lacked nalP. Deletion of nalP often resulted from recombination events between flanking repetitive elements. PolyC tract lengths ranged from 6–15 bp in nalP and 6–14 bp in mspA. In an examination of PV status, 58.8% of carriage, and 40.1% of invasive nalP-positive MenB isolates were nalP phase ON. The frequency of this phenotype was not significantly different in serogroup Y (MenY) carriage strains, but was significantly higher in invasive MenY strains (86.3%; p<0.0001). Approximately 90% of MenB carriage and invasive isolates were mspA phase ON; significantly more than MenY carriage (32.7%) or invasive (13.7%) isolates. This differential expression resulted from different mode mspA tract lengths between the serogroups. Our data indicates a differential requirement for NalP and MspA expression in MenB and MenY strains and is a step towards understanding the contributions of phase-variable loci to meningococcal biology.     

Conjugative Plasmids of Neisseria gonorrhoeae

Many clinical isolates of the human pathogen Neisseria gonorrhoeae contain conjugative plasmids. The host range of these plasmids is limited to Neisseria species, but presence of a tetracycline (tetM) determinant inserted in several of these plasmids is an important cause of the rapid spread of tetracycline resistance. Previously plasmids with different backbones (Dutch and American type backbones) and with and without different tetM determinants (Dutch and American type tetM determinants) have been identified. Within the isolates tested, all plasmids with American or Dutch type tetM determinants contained a Dutch type plasmid backbone. This demonstrated that tetM determinants should not be used to differentiate between conjugal plasmid backbones. The nucleotide sequences of conjugative plasmids with Dutch type plasmid backbones either not containing the tetM determinant (pEP5233) or containing Dutch (pEP5289) or American (pEP5050) type tetM determinants were determined. Analysis of the backbone sequences showed that they belong to a novel IncP1 subfamily divergent from the IncP1α, β, γ, δ and ε subfamilies. The tetM determinants were inserted in a genetic load region found in all these plasmids. Insertion was accompanied by the insertion of a gene with an unknown function, and rearrangement of a toxin/antitoxin gene cluster. The genetic load region contains two toxin/antitoxins of the Zeta/Epsilon toxin/antitoxin family previously only found in Gram positive organisms and the virulence associated protein D of the VapD/VapX toxin/antitoxin family. Remarkably, presence of VapX of pJD1, a small cryptic neisserial plasmid, in the acceptor strain strongly increased the conjugation efficiency, suggesting that it functions as an antitoxin for the conjugative plasmid. The presence of the toxin and antitoxin on different plasmids might explain why the host range of this IncP1 plasmid is limited to Neisseria species. The isolated plasmids conjugated efficiently between N. gonorrhoeae strains, but did not enhance transfer of a genetic marker.     

Tupaia Belangeri as an Experimental Animal Model for Viral Infection

Tupaias, or tree shrews, are small mammals that are similar in appearance to squirrels. The morphological and behavioral characteristics of the group have been extensively characterized, and despite previously being classified as primates, recent studies have placed the group in its own family, the Tupaiidae. Genomic analysis has revealed that the genus Tupaia is closer to humans than it is to rodents. In addition, tupaias are susceptible to hepatitis B virus and hepatitis C virus. The only other experimental animal that has been demonstrated to be sensitive to both of these viruses is the chimpanzee, but restrictions on animal testing have meant that experiments using chimpanzees have become almost impossible. Consequently, the development of the tupaia for use as an animal infection model could become a powerful tool for hepatitis virus research and in preclinical studies on drug development.     

Characterization of S3Pvac Anti-Cysticercosis Vaccine Components: Implications for the Development of an Anti-Cestodiasis Vaccine

Background

Cysticercosis and hydatidosis seriously affect human health and are responsible for considerable economic loss in animal husbandry in non-developed and developed countries. S3Pvac and EG95 are the only field trial-tested vaccine candidates against cysticercosis and hydatidosis, respectively. S3Pvac is composed of three peptides (KETc1, GK1 and KETc12), originally identified in a Taenia crassiceps cDNA library. S3Pvac synthetically and recombinantly expressed is effective against experimentally and naturally acquired cysticercosis.

Methodology/Principal Findings

In this study, the homologous sequences of two of the S3Pvac peptides, GK1 and KETc1, were identified and further characterized in Taenia crassiceps WFU, Taenia solium, Taenia saginata, Echinococcus granulosus and Echinococcus multilocularis. Comparisons of the nucleotide and amino acid sequences coding for KETc1 and GK1 revealed significant homologies in these species. The predicted secondary structure of GK1 is almost identical between the species, while some differences were observed in the C terminal region of KETc1 according to 3D modeling. A KETc1 variant with a deletion of three C-terminal amino acids protected to the same extent against experimental murine cysticercosis as the entire peptide. On the contrary, immunization with the truncated GK1 failed to induce protection. Immunolocalization studies revealed the non stage-specificity of the two S3Pvac epitopes and their persistence in the larval tegument of all species and in Taenia adult tapeworms.

Conclusions/Significance

These results indicate that GK1 and KETc1 may be considered candidates to be included in the formulation of a multivalent and multistage vaccine against these cestodiases because of their enhancing effects on other available vaccine candidates.     

汉坦病毒疫苗研制进展

本文从脑组织灭活疫苗、培养细胞单双价灭活疫苗、基因重组疫苗、DNA疫苗、减毒活疫苗、佐剂、灭活方法、免疫策略等方面概述了汉坦病毒疫苗研制近况。     

汉坦病毒疫苗研制进展

本文从脑组织灭活疫苗、培养细胞单双价灭活疫苗、基因重组疫苗、DNA疫苗、减毒活疫苗、佐剂、灭活方法、免疫策略等方面概述了汉坦病毒疫苗研制近况.     

Development of the BG-Malaria trap as an alternative to human-landing catches for the capture of Anopheles darlingi

Although the human-landing catch (HLC) method is the most effective forcollecting anthropophilic anophelines, it has been increasingly abandoned,primarily for ethical considerations. The objective of the present study was todevelop a new trap for the collection of Anopheles darlingi .The initial trials were conducted using the BG-Sentinel trap as a standard forfurther trap development based on colour, airflow direction and illumination.The performance of the trap was then compared with those of the CDC, Fay-Prince,counterflow geometry trap (CFG) and HLC. All trials were conducted outdoorsbetween 06:00 pm-08:00 pm. Female specimens of An. darlingiwere dissected to determine their parity. A total of 8,334 anophelines werecaptured, of which 4,945 were identified as An. darlingi . Thebest trap configuration was an all-white version, with an upward airflow and norequired light source. This configuration was subsequently named BG-Malaria(BGM). The BGM captured significantly more anophelines than any of the othertraps tested and was similar to HLC with respect to the number and parity ofanophelines. The BGM trap can be used as an alternative to HLC for collectinganophelines.     

Demonstration of Multiple Mating in Heterodera glycines with Biochemical Markers

Controlled crosses of Heterodera glycines were carried out by placing one o r more virgin females of known esterase phenotype on an agar plate and adding, at various time intervals, one or more males of different esterase phenotypes. Progeny (second-stage juveniles) of such crosses were propagated on soybeans, and 30 days later young females were subjected to electrophoretic analysis to determine their esterase phenotype. Esterase phenotypes that represented the heterozygous state of the maternal and paternal genomes confirmed the hybrid nature of the progeny and identified their male parent. When each of 74 females was given the opportunity to mate successively with two males of different esterase phenotypes, 43 mated with a single male and 31 mated with both males. One female mated with three males, i.e., with a male of its own population (sib mating) and the two males provided for the cross. Inseminated females could mate for a second time soon after, or as late as 24 hours after, their first mating. When single males were given the opportunity to mate with many females, about equal numbers of them inseminated zero, one, two, or three females. In greenhouse tests, 12 females were given the opportunity to mate with many males of three different esterase phenotypes. Two females mated with one and possibly more males of the same phenotype, and 10 females mated with males of two different esterase phenotypes. In conclusion, multiple mating appears to be a common behavior of males and females of H. glycines.     

Development of an Optimal Diaphragmatic Hernia Rabbit Model for Pediatric Thoracoscopic Training

Our objectives were to standarize the procedure needed to reproduce a similar surgicalscene which a pediatric surgeon would face on repairing a Bochdalek hernia in newborns andto define the optimal time period for hernia development that achieve a realistic surgicalscenario with minimimal animal suffering. Twenty New Zealand white rabbits weighing 3–3.5kg were divided into four groups depending on the time frame since hernia creation tothoracoscopic repair: 48 h, 72 h, 96 h and 30 days. Bochdalek trigono was identified andprocedures for hernia creation and thoracoscopic repair were standarized. Blood wascollected for hematology (red blood cells, white blood cells, platelets, hemoglobin andhematocrit), biochemistry (blood urea nitrogen, creatinine, alanine aminotransferase,aspartate aminotransferase, lactate dehydrogenase and creatine kinase) and gas analysis(arterial blood pH, partial pressure of oxygen, partial pressure of carbón dioxide, oxygensaturation and bicarbonate) at baseline and before the surgial repairment. Glucocorticoidmetabolites concentration in faeces was measured. Thoracoscopy video recordings wereevaluated by six pediatric surgeons and rated from 0 to 10 according to similarities withcongenital diaphragmatic hernia in newborn and with its thoracoscopic approach.Statistical methods included the analysis of variance, and comparisons between groups werefollowed by a post-hoc Tukey’s test. Fourty -eight h showed to be the optimal time frameto obtain a diaphragmatic hernia similar to newborn scenario from a surgical point of viewwith minimal stress for the animals.     

Functional Analysis of the Gonococcal Genetic Island of Neisseria gonorrhoeae

Neisseria gonorrhoeae is an obligate human pathogen that is responsible for the sexually-transmitted disease gonorrhea. N. gonorrhoeae encodes a T4SS within the Gonococcal Genetic Island (GGI), which secretes ssDNA directly into the external milieu. Type IV secretion systems (T4SSs) play a role in horizontal gene transfer and delivery of effector molecules into target cells. We demonstrate that GGI-like T4SSs are present in other β-proteobacteria, as well as in α- and γ-proteobacteria. Sequence comparison of GGI-like T4SSs reveals that the GGI-like T4SSs form a highly conserved unit that can be found located both on chromosomes and on plasmids. To better understand the mechanism of DNA secretion by N. gonorrhoeae, we performed mutagenesis of all genes encoded within the GGI, and studied the effects of these mutations on DNA secretion. We show that genes required for DNA secretion are encoded within the yaa-atlA and parA-parB regions, while genes encoded in the yfeB-exp1 region could be deleted without any effect on DNA secretion. Genes essential for DNA secretion are encoded within at least four different operons.