The UspA1 protein and a second type of UspA2 protein mediate adherence of Moraxella catarrhalis to human epithelial cells in vitro

The UspA1 and UspA2 proteins of Moraxella catarrhalis are structurally rela ted, are exposed on the bacterial cell surface, and migrate as very high-mo lecular-weight complexes in sodium dodecyl sulfate-polyacrylamide gel elect rophoresis. Previous analysis of uspA1 and uspA2 mutants of M. catarrhalis strain 035E indicated that UspA1 was involved in adherence of this organism to Chang conjunctival epithelial cells in vitro and that expression of Usp A2 was essential for resistance of this strain to killing by normal human s erum (C. Aebi, E. R. Lafontaine, L. D. Cope, J. L. Latimer, S. R. Lumbley, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 66:3113-3119, 1998). In the present study, isogenic uspA1, uspA2, and usA1 uspA2 mutations were constructed in three additional M. catarrhalis strains: 012E, TTA37, and 0 46E. The aspA1 mutant of strain 012E had a decreased ability to attach to C hang cells. However, inactivation of the uspA1 gene in both strain TTA37 an d strain 046E did not cause a significant decrease in attachment ability. I nactivation of the uspA2 gene of strain TTA37 did result in a loss of attac hment ability. Nucleotide sequence analysis revealed that the predicted pro tein encoded by the uspA2 genes of both strains TTA37 and 046E had a N-term inal half that resembled the N-terminal half of uspA1 proteins, whereas the C-terminal half of this protein was nearly identical to those of previousl y characterized UspA2 proteins. The gene encoding this "hybrid" protein was designated uspA2H. PCR-based analysis revealed that approximately 20% of M . catarrhalis strains apparently possess a uspA2H gene instead of a uspA2 g ene. The M. catarrhalis uspA1, uspA2, and uspA2H genes were cloned and expr essed in Haemophilus influenzae cells, which were used to prove that both t he UspA1 and UspA2H proteins can function as adhesins in vitro.