Regulation effect of CcpA protein on the biosynthesis of capsular polysaccharide in Streptococcus pneumoniae

Abstract:

Abstract:［Objective］We studied the regulation effect of glycometabolic protein，catabolite control protein A (CcpA)，on the biosynthesis of capsular polysaccharide (CPS) in Streptococcus pneumonia．［Methods］His-tagged CcpA protein was expressed in E．coli BL21(DE3) and purified by Ni2 + affinity chromatography．The anti-CcpA serum was obtained from immunized mice and the antibody titer was determined by ELISA．The conservation of CcpA was determined by Western blotting． In addition，binding of CcpA protein to the promoter region of cps locus was verified by EMSA． The amount of capsular polysaccharide was determined by ELISA and compared among wild type D39 strain，ccpA mutant and the complement strains．［Results］CcpA protein was conserved in different pneuococcal serotypes included in this study．EMSA assay revealed that CcpA protein could bind the promoter region of the cps locus in a dose-dependent manner．The absence of ccpA gene led to an increased expression of capsular polysaccharide，and complement expression of CcpA protein significantly reduced the amount of capsular polysaccharide．［Conclusion］ CcpA is conserved in Streptococcus pneumonia，which plays a role in regulation of the expression of the capsular polysaccharide.