Profiling the Membrane and Glycosaminoglycan-Binding Proteomes of Moraxella catarrhalis.

Moraxella catarrhalis, a Gram-negative bacterium, is an important respiratory pathogen causing acute otitis media and exacerbations of chronic obstructive pulmonary disease. Adhesion of the pathogen to human epithelial cells is mediated via bacterial membrane adhesin proteins. To identify the surface proteome of Moraxella catarrhalis, we applied different membrane protein extraction methods in combination with different proteomic technologies. Proteins from preparations of outer membrane vesicles and from carbonate extractions were analyzed using either a gel-based nano-HPLC-MS/MS technique or 2D-LC-MS/MS. Furthermore, because glycosaminoglycans (GAGs) play an important role for microbial entry into human cells, the GAG-binding membranome of Moraxella catarrhalis was investigated using a glycan-based pull-down approach. By these means, potential vaccine protein candidates that were previously selected by the ANTIGENome technology were confirmed, but importantly also novel proteins were identified as candidates.

Comprehensive antigen screening identifies Moraxella catarrhalis proteins that induce protection in a mouse pulmonary clearance model.

Moraxella catarrhalis is one of the three most common causative bacterial pathogens of otitis media, however no effective vaccine against M. catarrhalis has been developed so far. To identify M. catarrhalis vaccine candidate antigens, we used carefully selected sera from children with otitis media and healthy individuals to screen small-fragment genomic libraries that are expressed to display frame-selected peptides on a bacterial cell surface. This ANTIGENome technology led to the identification of 214 antigens, 23 of which were selected by in vitro or in vivo studies for additional characterization. Eight of the 23 candidates were tested in a Moraxella mouse pulmonary clearance model, and 3 of these antigens induced significantly faster bacterial clearance compared to adjuvant or to the previously characterized antigen OmpCD. The most significant protection data were obtained with the antigen MCR_1416 (Msp22), which was further investigated for its biological function by in vitro studies suggesting that Msp22 is a heme binding protein. This study comprises one of the most exhaustive studies to identify potential vaccine candidate antigens against the bacterial pathogen M. catarrhalis.