Identification of hemagglutinin protein from Streptococcus pneumoniae pili as a vaccine candidate by proteomic analysis

Introduction: Streptococcus pneumoniae is a Gram-positive, bacterial human pathogen that causes a large number of respiratory tract infections, such as pneumonia and sinusitis, as well as invasive diseases such as septicemia and meningitis. Among the surface-exposed virulence factors, the pneumococcal pilus has been shown to play a role in host-cell adhesion. Hemagglutinin activity has been shown to correlate with adhesion ability. The purpose of this study was to identify of S. pneumoniae pili proteins with hemagglutinin activity, and to proteonomically analyze such proteins as potential vaccine candidates. Materials and Methods: The purification of pili was carried out by a pilus cutter method. After SDS-PAGE separation, pili proteins were purified by electroelution and dialysis. After a hemagglutinination assay with mouse erythrocytes, the hemagglutinin protein was identified with Liquid Chromatography/Mass Spectrometry, along with assessments of antigenicity and epitope mapping. Results: SDS-PAGE showed that pili protein had major bands of molecular weights of 67, 54, 25, and 11 kDa. The 54 kDa pili protein was the hemagglutinin. Computational bioinformatics analysis by Mascot Server revealed this hemagglutinin matched with the Rrgb protein of S. pneumoniae (gi: 299856655). Conclusion: The analysis of its antigenicity, and epitope mapping showed that a novel protein was identified as the pilus backbone (Rrgb) of Streptococcus pneumoniae, and has a high antigenicity suitable for further development as a vaccine candidate.