Identification of multiple linear epitopes of the plasminogen activator A (PauA) of Streptococcus uberis with murine monoclonal antibodies

Streptococcus (S.) uberis is a common cause of mastitis in cattle. A protein (PauA) secreted by this bacterium is capable of activating plasminogen from sheep and cattle. The PauA first binds to bovine plasminogen (b-plg) to form a PauA–plasminogen complex that subsequently binds to and activates b-plg to form plasmin. We have identified several linear epitopes of PauA that are recognized by murine monoclonal antibodies to PauA. Two of the monoclonal antibodies which neutralized the enzymatic activity of PauA, EC3 and 2.22, recognized common linear peptide sequences with similar charge and spacing patterns. These neutralization epitopes are located in the predicted α-domain of the PauA molecule. Further, these same epitopes are in critical structure/function domains identified in other studies. These characterizations may facilitate the design of an efficacious vaccine for streptococcal mastitis in the dairy cow.