Prospects offered by genome studies for combating meningococcal disease by vaccination

Meningococcal serogroup B infections: a search for a broadly protective vaccine

Meningococcal disease is mainly caused by serogroup B in many West European countries. Recently, a highly efficacious vaccine against infections caused by serogroup C has been introduced in the UK and The Netherlands. However, an effective vaccine against serogroup B has not yet become available. Outer membrane vesicle vaccines against serogroup B were previously tested in large Phase III trials but showed a low efficacy in young children. In addition, the high variability of the vaccines' main component, porin A, potentially diminishes its efficacy. Therefore, several approaches in either optimizing these outer membrane vesicle vaccines or searching for novel, highly conserved antigens are currently under investigation. The sequencing of the meningococcal genome has provided new opportunities to detect additional immunogenic epitopes. In this review, the developments in the search for a broadly protective meningococcal serogroup B vaccine will be discussed.

Methionine sulfoxide reductases in prokaryotes

In living organisms, most methionine residues exposed to reactive oxygen species (ROS) are converted to methionine sulfoxides. This reaction can lead to structural modifications and/or inactivation of proteins. Recent years have brought a wealth of new information on methionine sulfoxide reductase A (MsrA) and B (MsrB) which makes methionine oxidation a reversible process. Homologs of msrA and msrB genes have been identified in most living organisms and their evolution throughout different species led to different genetic organization and different copy number per organism. While MsrA and MsrB had been the focus of multiple biochemical investigations, our understanding of their physiological role in vivo remains scarce. Yet, the recent identification of a direct link between protein targeting and MsrA/MsrB repair offers a best illustration of the physiological importance of this pathway. Repeatedly identified as a potential "virulence factor", contribution of msrA to pathogenicity is also discussed. It remains, however, unclear whether reduced virulence results from overall viability loss or relates to specific oxidized virulence factors left unrepaired. We speculate that a major issue towards assessing the in vivo role of the MsrA/MsrB repair pathway in the next future will be to decipher the interrelations, if any, between MsrA/MsrB-mediated repair and chaperone-assisted folding and/or protease-assisted degradation.

A recombinant beta-1,3-glucanosyltransferase homolog of Coccidioides posadasii protects mice against coccidioidomycosis

Coccidioides posadasii is a fungal respiratory pathogen which is responsible for recurrent epidemics of San Joaquin Valley fever (coccidioidomycosis) in desert regions of the southwestern United States. Numerous studies have revealed that the cell wall of the parasitic phase of the fungus is a reservoir of immunoreactive macromolecules and a potential source of a vaccine against this mycosis. A 495-bp fragment of a C. posadasii gene which encodes a putative wall-associated, glycosylphosphatidylinositol (GPI)-anchored beta-1,3-glucanosyltransferase was identified by computational analysis of the partially sequenced genome of this pathogen. The translated, full-length gene (GEL1) showed high sequence homology to a reported beta-1,3-glucanosyltransferase of Aspergillus fumigatus (70% identity, 90% similarity) and was selected for further study. The GEL1 mRNA of C. posadasii was detected at the highest level during the endosporulation stage of the parasitic cycle, and the mature protein was immunolocalized to the surface of endospores. BALB/c or C57BL/6 mice were immunized subcutaneously with the bacterium-expressed recombinant protein (rGel1p) to evaluate its protective efficacy against a lethal challenge of C. posadasii by either the intraperitoneal or intranasal route. In both cases, rGel1p-immune mice infected with the pathogen showed a significant reduction in fungal burden and increased survival compared to nonimmune mice. The recombinant beta-1,3-glucanosyltransferase is a valuable addition to an arsenal of immunoreactive proteins which could be incorporated into a human vaccine against coccidioidomycosis.