Characterization of the Moraxella catarrhalis Hag Adhesin
Moraxella catarrhalis is a Gram-negative unencapsulated pathogen of the human respiratory system. This pathogen is responsible for ~20% of the otitis media cases and ~10% of all exacerbations of chronic obstructive pulmonary disease in the United States. To complicate matters, greater than 90% of all M. catarrhalis isolates examined to date are resistant to the â-lactam class of antibiotics, and therefore, a vaccine that elicits an immune response against this pathogen is highly desirable. To that end, the work presented here focuses on examining the feasibility of the Hag adhesin from M. catarrhalis as a vaccine antigen. Previous work has shown that Hag is a large, 2000 amino acid, autotransporter protein and that mediates M. catarrhalis attachment to A549 and human middle ear epithelial cells. Hag also has been shown to form oligomers and is responsible for lollipop like projections on the M. catarrhalis surface. In order to further explore Hag’s characteristics, four M. catarrhalis strains were assayed for the ability to bind to pathogenically relevant cells, namely A549 (lung), NCIH292 (lung), HMEE (middle ear) and Chang (conjunctival) cell lines. This work revealed that Hag is necessary for attachment to all four of these cells lines. When Hag was expressed in non-adherent E. coli, it was able to mediate attachment to collagen as well as NCIH292 and HMEE cells. When the hag genes from seven M. catarrhalis isolated were analyzed, it was observed that the encoded protein products contained predicted motifs that were structurally similar to those found in YadA from Yersinia enterocolitica, the prototypical trimeric autotransporter. Previous work had shown that YadA forms lollipop like structure on the Y. enterocolitica surface and that attachment to epithelial cells and collagen is mediated through an N-terminal globular head. When Hag mutants lacking this head structure were expressed in E. coli, these bacteria were still able to bind to epithelial cells and collagen. Further analysis revealed that unlike YadA, Hag mediates attachment to epithelial cells and collagen in separate regions within the stalk of the protein.
School:University of Toledo Health Science Campus
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:moraxella catarrhalis otitis media hag copd bacterial adhesins
Date of Publication:01/01/2007