Analysis of a trimeric autotransporter adhesin from Mannheimia haemolytica A1

A putative adhesin, Ahs, has been hypothesized to play a role in the attachment of Mannheimia haemolytica A1 within the bovine lung during bovine pneumonic pasteurellosis. Sequence analysis revealed conserved collagen binding motifs in the adhesin AhsA. M. haemolytica SH1217 adhered to collagen in vitro and antibody inhibition showed that AhsA is specifically involved in this interaction. Calf respiratory tract cells bound to a M. haemolytica protein of 70 kDa, corresponding to the size of AhsA. AhsB was found to have conserved sequences involved in trimerization and outer membrane localization. The C-terminal 120 amino acids of AhsB were shown to trimerize and did not dissociate in standard denaturing conditions, both aspects seen for known trimeric autotransporters. These studies support the hypothesis that the proteins translated from the ahs locus form a trimeric autotransporter adhesin composed of the passenger adhesin AhsA, and the trimerizing translocator AhsB.