Predicted proteins of Neisseria meningitidis as potential vaccine candidates: from in silico analyses to experimental corroboration

Neisseria meningitidis serogroup B infections are a serious health threat to the world that cannot be prevented by vaccination. Here, we report an analysis of the MC58 Neisseria meningitidis genome aimed at the identification of new potential vaccine candidates. 'Hypothetical' and 'conserved hypothetical' annotated genes, together with those with putative functions related to the cell envelope, were subjected to extensive sequence similarity searches, as well as motif, cellular location, and domain analyses complemented with manual curation. As a result, a set of 35 unchar- acterized ORFs, predicted to encode for surface exposed or virulence related proteins, was identified. The candidates were subdivided in three categories: 1) predicted outer membrane proteins (OMPs) unique of the Neisseria genus; 2) conserved OMPs from various genus and 3) proteins homologous to known OMPs or to proteins previously found to be immunogenic in animal models. Two of the final candidates, nmb1126 and nmb0181, were cloned and expressed in Escherichia coli. The resulting products were purified by Metal Chelating Chromatography and used to immunize mice. The recombinant proteins were capable of inducing antibodies against the native antigen in preparations of a panel of three strains and displayed bactericidal activity against the homologous strains.