[Prokaryotic expression of recombinant Streptococcus suis IgG binding protein and its binding activity with IgG]

Streptococcus suis (S. suis) IgG-binding protein (SPG) was present in all S. suis strains examined. It showed binding activities with IgG from various host species. Little was known about the biological role of this protein, but it was commonly believed that it acted as virulence factor. In this study, the genes encoding SPG were amplified respectively from the total DNA of the S. suis serotype 1/2, 1, 2 and 9 with PCR and expressed in Escherichia coli BL21 by plasmid pET28a as vector. The recombinant proteins were first purified with affinity chromatography (Ni-NTA), and further purified by sephadexG-200 gel chromatography. The recombinant SPG proteins were identified to have binding activities with IgG of different host species, and for human and porcine IgG they showed better binding activities. But the SPG from different serotypes of S. suis showed no great differences in their binding activities with IgG from the same host species.