Identification of intrinsic and extrinsic membrane proteins bearing surface epitopes of Mycoplasma hyopneumoniae.

A library of monoclonal antibodies (McAbs) raised against Mycoplasma hyopneumoniae was screened to select McAbs that bound both to surface epitopes on intact organisms and to corresponding proteins identified by immunoblot analysis. Four proteins (indicated by MW in kilodaltons) were established as surface antigens: p65, p50, p44 and p41. Triton X-114 detergent phase fractionation of whole organisms clearly distinguished p65, p50 and p44 as hydrophobic integral membrane proteins, whereas p41 was identified as a hydrophilic surface protein apparently extrinsic to the membrane. This technique also provided a rapid and efficient method for isolating the relatively small number of hydrophobic proteins associated with M. hyopneumoniae. Preliminary evidence suggests that p65, p50 and p44 are linked covalently to lipids, which may be important in dictating their interaction with the membrane. Immunoblot analysis of antibodies from swine immunized with M. hyopneumoniae also suggests that p65 and p44 may be "immunodominant" antigens in this host.