Identification of B cell epitopes in the MSG1 protein of Mycoplasma suis.

Mycoplasma suis (M. suis) is an extracellular bacterial organism that attaches to and causes deformity and damage to porcine red blood cells. M. suis glyceraldehyde-3-phosphate dehydrogenase-like protein 1 (MSG1), a membrane-associated adhesion protein, plays a major role in M. suis attachment and infection of porcine erythrocytes. In order to identify the epitopes in MSG1 protein of M. suis, recombinant MSG1 (rMSG1) expressed in Escherichia coli Top10 was purified with affinity chromatography and used to immunize BALB/c mice to prepare and screen monoclonal antibodies (MAbs). Western blot results showed that 1C10, 2F10, 4G10, and 10E9 can specifically react with recombinant MSG1 and M. suis. Moreover, 23 truncated fragments of MSG1 were amplified and cloned into pET-32a vector and induced by IPTG. Different recombinant truncated proteins were used to identify B cell epitopes in the rMSG1 protein. Epitope mapping revealed that MAb 1C10 recognizes the linear epitope D(291)THGSVF(297); MAb 2F10 recognizes the linear epitope L(251)CLKI(255); and MAbs 4G10 and 10E9 recognize the linear epitope I(268)KDGENE(274). The alignment of MSG1 epitope sequences with that of different M. suis strains accessed on NCBI showed that one epitope is highly conserved in M. suis strains. This research is the first to examine the epitopes in MSG1 of M. suis and demonstrate the variations of epitopes.