Outer membrane protein D15 is conserved among Haemophilus influenzae species and may represent a universal protective antigen against invasive disease

The evolutionary origin of the protein-translocating channel of chloroplastic envelope membranes: identification of a cyanobacterial homolog

The known envelope membrane proteins of the chloroplastic protein import apparatus lack sequence similarity to proteins of other eukaryotic or prokaryotic protein transport systems. However, we detected a putative homolog of the gene encoding Toc75, the protein-translocating channel from the outer envelope membrane of pea chloroplasts, in the genome of the cyanobacterium Synechocystis sp. PCC 6803. We investigated whether the low sequence identity of 21% reflects a structural and functional relationship between the two proteins. We provide evidence that the cyanobacterial protein is also localized in the outer membrane. From this information and the similarity of the predicted secondary structures, we conclude that Toc75 and the cyanobacterial protein, referred to as SynToc75, are structural homologs. synToc75 is essential, as homozygous null mutants were not recovered after directed mutagenesis. Sequence analysis indicates that SynToc75 belongs to a family of outer membrane proteins from Gram-negative bacteria whose function is not yet known. However, we demonstrate that these proteins are related to a specific group of prokaryotic secretion channels that transfer virulence factors, such as hemolysins and adhesins, across the outer membrane.

A 20-kilodalton N-terminal fragment of the D15 protein contains a protective epitope(s) against Haemophilus influenzae type a and type b

A conserved 80-kDa minor outer membrane protein, D15, of Haemophilus influenzae has been shown to be a protective antigen in laboratory animals against H. influenzae type a (Hia) or type b (Hib) infection. To localize the protective B-cell epitope(s) within the D15 protein and to further explore the possibility of using synthetic peptides as vaccine antigens, a 20-kDa N-terminal fragment of D15 protein (truncated D15 [tD15]) was expressed as a fusion protein with glutathione S-transferase in Escherichia coli. The tD15 moiety was cleaved from glutathione S-transferase by using thrombin and purified to homogeneity. The purified soluble tD15 appeared to contain immunodominant protective epitope(s) against Hia and Hib, since rabbit antisera directed against tD15 were capable of protecting infant rats from Hia or Hib bacteremia. The ease of purification of soluble tD15, therefore, makes it a better candidate antigen than the full-length recombinant D15 which is produced as inclusion bodies in E. coli. Furthermore, both the purified tD15 fragment and a mixture of tD15-derived peptides spanning amino acid residues 93 to 209 of the mature D15 protein were capable of inhibiting the protection against Hib conferred on infant rats by rabbit anti-tD15 antiserum, indicating that the protective epitopes of D15 may not be conformational. However, the administration of pooled rabbit immune sera raised against the same panel of peptides failed to protect infant rats from Hib infection.

Omp85 proteins of Neisseria gonorrhoeae and Neisseria meningitidis are similar to Haemophilus influenzae D-15-Ag and Pasteurella multocida Oma87

The genes encoding homologous 85 kDa outer membrane proteins of Neisseria gonorrhoeae and Neisseria meningitidis have been cloned and sequenced. The gonococcal gene, omp85, was identified by screening a genomic library with an antiserum raised against purified gonococcal outer membranes. The gene encoded a 792 amino acid protein, Omp85, having a typical signal peptide and a carboxyl-terminal phenylalanine characteristic of outer membrane proteins. The amino acid sequence was similar to that of the D15 protective surface antigen (D-15-Ag) of Haemophilus influenzae, and the Oma87 of Pasteurella multocida. Southern analysis demonstrated that omp85 was present as a single copy in N. gonorrhoeae and N. meningitidis. PCR amplification was used to obtain a clone of the N. meningitidis omp85 homologue. Sequence analysis revealed that the N. meningitidis Omp85 was 95% identical to the N. gonorrhoeae Omp85.

Nontypeable Haemophilus influenzae: pathogenesis and prevention

In this paper, we describe the ability of nontypeable Haemophilus influenzae (NTHi) to coexist with the human host and the devastating results associated with disruption of the delicate state of balanced pathogenesis, resulting in both acute and chronic respiratory tract infections. It has been seen that the strains of NTHi causing disease show a marked genetic and phenotypic diversity but that changes in the lipooligosaccharide (LOS) and protein size and antigenicity in chronically infected individuals indicate that individual strains of NTHi can remain and adapt themselves to avoid expulsion from their infective niche. The lack of reliance of NTHi on a single mechanism of attachment and its ability to interact with the host with rapid responses to its environment confirmed the success of this organism as both a colonizer and a pathogen. In vitro experiments on cell and organ cultures, combined with otitis media and pulmonary models in chinchillas, rats, and mice, have allowed investigations into individual interactions between NTHi and the mammalian host. The host-organism interaction appears to be a two-way process, with NTHi using cell surface structures to directly interact with the mammalian host and using secreted proteins and LOS to change the mammalian host in order to pave the way for colonization and invasion. Many experiments have also noted that immune system evasion through antigenic variation, secretion of enzymes and epithelial cell invasion allowed NTHi to survive for longer periods despite a specific immune response being mounted to infection. Several outer membrane proteins and LOS derivatives are discussed in relation to their efficacy in preventing pulmonary infections and otitis media in animals. General host responses with respect to age, genetic makeup, and vaccine delivery routes are considered, and a mucosal vaccine strategy is suggested.