[Enolase of Streptococcus suis serotype 2 is involved in the antiphagocytosis of Streptococcus suis].

Objective: To prepare the recombinant enolase of Streptococcus suis (SsEno), analyze the effect of SsEno on the antiphagocytosis by antibody-blocking assay in the human blood bactericidal model, and identify the human fibrinogen (hFg)-binding activity of SsEno protein.
Methods: SsEno gene was amplified using the primers designed according to 05ZYH33 genome sequences and cloned into the expression vector pET28a to construct recombinant plasmids. The plasmids were transformed into E.coli BL21(DE3) and induced to express by IPTG. The expression level was analyzed by SDS-PAGE. The recombinant proteins were purified by nickel affinity chromatography and identified by Western blotting. High-titer specific antiserum against SsEno was prepared by immunizing rabbits with the purified recombinant proteins. The impact of SsEno on antiphagocytosis was analyzed by antibody-blocking assay in the human blood bactericidal model. In addition, the specific binding activity with hFg was identified by Far-Western blotting and ELISA.
Results: The prokaryotic expression vector of hisSsEno (SsEno with His tag) was constructed and high-purity recombinant expressed protein was purified. In specific antibody blocking assay, antiserum against the SsEno significantly decreased the percent of survival bacteria as observed in high virulent strain 05ZYH33. Additionally, hisSsEno was proved to have the specific binding activity with hFg.
Conclusion: SsEno was found to be a potential antiphagocytic factor of S. suis with a specific binding to hFg, suggesting that SsEno play an important role in antiphagocytosis of S. suis.