The outer membrane protein OmpA of Mannheimia haemolytica A1 is involved in the binding of fibronectin.

An enzyme-linked immunosorbent assay using bovine fibronectin as the substrate was used to demonstrate that Mannheimia haemolytica A1 binds to fibronectin. This binding to fibronectin was specific as no binding was observed with bovine fibrinogen. The binding to fibronectin was not observed if the M. haemolytica A1 cells were pretreated with trypsin or proteinase K, suggesting that it involved a protein molecule on the cell surface. Interestingly, the fibronectin-binding activity was found to be higher in an acapsular mutant compared with its parent strain. The fibronectin-binding protein was shown to be present in the outer membrane fraction of M. haemolytica A1. A 45 kDa outer membrane protein that binds to fibronectin was identified by Far-Western immunoblot analysis. This protein was purified and subjected to MS matrix-assisted laser desorption ionization time-of-flight analysis. The results identified it to be outer membrane OmpA based on comparison with the M. haemolytica A1 genomic sequence.