Analysis of a collagen-binding trimeric autotransporter adhesin from Mannheimia haemolytica A1

A locus that codes for a high-molecular-weight adhesin was previously isolated from Mannheimia haemolytica A1. In this study, we showed that this locus, named ahs, codes for two proteins (AhsA and AhsB) that exhibit characteristics of a trimeric autotransporter adhesin. Sequence analysis of AhsA showed the presence of 21 collagen-binding motifs in the protein. Collagen-binding assays showed that M. haemolytica A1 binds to collagen in a dose-dependent manner. This binding activity is trypsin sensitive and can be inhibited by anti-AhsA antibody. AhsB is the cognate transporter for AhsA. The C-terminal of AhsB showed highly conserved amino acids typical of trimeric autotransporters. Experimental data showed that the C-terminal 120 amino acids of AhsB could indeed form trimeric molecules. Western immunoblots showed the presence of anti-AhsA antibodies in the sera of calves that had been challenged with M. haemolytica A1, suggesting that AhsA is expressed and immunogenic in cattle.