Intermolecular relationships of major surface proteins of Anaplasma marginale

Immunization with Anaplasma marginale membranes containing major surface proteins (MSPs) induces protective immunity against clinical disease (N. Tebele, T. C. McGuire, and G. H. Palmer, Infect. Immun. 59:3199-3204, 1991). For use in design of a recombinant antigen subunit vaccine for A. marginale, intermolecular relationships of known A. marginale MSPs were analyzed. Under nonreducing conditions, MSP-2 and MSP-5 occur as multimers. A large (> 300-kDa-molecular-mass), nonreduced protein complex contained MSP-1a linked by disulfide bonds to MSP-1b and by noncovalent bonds to MSP-5. MSP-2 was also noncovalently bound to this complex. The nearest neighbor membrane proteins were identified by cross-linking reactions followed by immunoblotting with anti-MSP antibodies. A cross-linked aggregate retained in the stacking gel contained MSP-1a, MSP-1b, MSP-2, MSP-3, MSP-4, and MSP-5. Collectively, the data indicate that MSP-2 and MSP-5 occur as monomers and disulfide-bonded multimers. The MSP-1 complex occurs as both disulfide-bonded and noncovalently associated MSP-1 and MSP-1b, and MSP-2 and MSP-5 are noncovalently associated with MSP-1. Also, MSP-1, MSP-2, MSP-3, and MSP-4 are nearest neighbors, and MSP-5 is noncovalently associated with this cross-linked complex.