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A protective epitope of Moraxella catarrhalis is encoded by two different genes
C Aebi1, I Maciver, J L Latimer
1Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235-9048, USA.
Abstract:
The high-molecular-weight UspA protein of Moraxella catarrhalis has been described as being both present on the surface of all M. catarrhalis disease isolates examined to date and a target for a monoclonal antibody (MAb 17C7) which enhanced pulmonary clearance of this organism in a mouse model system (M. E. Helminen et al., J. Infect. Dis. 170:867-872, 1994). A recombinant bacteriophage that formed plaques which bound MAb 17C7 was shown to contain a M. catarrhalis gene, designated uspA1, that encoded a protein with a calculated molecular weight of 88,271. Characterization of an isogenic uspA1 mutant revealed that elimination of expression of UspA1 did not eliminate the reactivity of M. catarrhalis with MAb 17C7. In addition, N-terminal amino acid analysis of internal peptides derived from native UspA protein and Southern blot analysis of M. catarrhalis chromosomal DNA suggested the existence of a second UspA-like protein. A combination of epitope mapping and ligation-based PCR methods identified a second M. catarrhalis gene, designated uspA2, which also encoded the MAb 17C7-reactive epitope. The UspA2 protein had a calculated molecular weight of 62,483. Both the isogenic uspA1 mutant and an isogenic uspA2 mutant possessed the ability to express a very-high-molecular-weight antigen that bound MAb 17C7. Southern blot analysis indicated that disease isolates of M. catarrhalis likely possess both uspA1 and uspA2 genes. Both UspA1 and UspA2 most closely resembled adhesins produced by other bacterial pathogens.
Insights
Moraxella catarrhalis possesses two UspA proteins, UspA1 and UspA2, which are surface adhesins. Both proteins bind to the monoclonal antibody 17C7, crucial for enhancing pulmonary clearance.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Immunology
Background:
- The UspA protein of Moraxella catarrhalis is a surface antigen present on disease isolates.
- Monoclonal antibody 17C7 targets UspA and enhances pulmonary clearance in a mouse model.
- Previous studies suggested UspA's role in M. catarrhalis pathogenesis.
Purpose of the Study:
- To identify and characterize the genes encoding the M. catarrhalis UspA protein.
- To investigate the existence of additional UspA-like proteins.
- To determine the role of these proteins in M. catarrhalis-host interactions.
Main Methods:
- Recombinant bacteriophage screening to identify UspA genes.
- Gene knockout mutagenesis to create isogenic mutants (uspA1 and uspA2).
- N-terminal amino acid sequencing, Southern blot analysis, and epitope mapping.
- Ligation-based PCR for gene identification.
Main Results:
- Two genes, uspA1 and uspA2, encoding UspA1 (88,271 Da) and UspA2 (62,483 Da) were identified.
- Both UspA1 and UspA2 contain the MAb 17C7-reactive epitope.
- Mutants lacking either uspA1 or uspA2 still expressed a high-molecular-weight antigen reactive with MAb 17C7.
- Disease isolates of M. catarrhalis typically possess both uspA1 and uspA2 genes.
- Both UspA1 and UspA2 proteins are structurally similar to adhesins from other bacterial pathogens.
Conclusions:
- Moraxella catarrhalis expresses at least two distinct UspA proteins, UspA1 and UspA2.
- Both UspA1 and UspA2 contribute to the reactivity with MAb 17C7.
- The presence of both genes in clinical isolates suggests their importance in M. catarrhalis infections.
- UspA proteins function as adhesins, potentially playing a role in bacterial colonization and virulence.