Codon Optimization, Prokaryotic Expression and Immunogenicity of Sip Protein from Streptococcus agalactiae
CHEN Zhi-Ting1,2,*, KE Xiao-Li2,*, ZHENG Shao-Ling3, LIU Zhi-Gang2, CHEN Gang1,**, LU Mai-Xin2,**
1 College of Fisheries, Guangdong Ocean University, Zhanjiang 524025, China; 2 Pearl River Fisheries Research Institute/Key Laboratory of Tropical &Subtropical Fishery Resource Application & Cultivation, Ministry of Agriculture and Rural Affairs, Chinese Academy of Fishery Science, Guangzhou 510380, China; 3 College of Animal Science and Technology, Zhongkai University of Agricultural Engineering, Guangzhou 510550, China
Abstract：Surface immunogenic protein (Sip) is a surface immunogenic protein of Streptococcus agalactiae, which can be used as a target for the potential vaccine antigen against S. agalactiae in tilapia (Oreochromis niloticus). In order to improve the expression level of recombinant Sip protein, the prokaryotic expression and immunogenicity analysis of codon optimized Sip protein from S. agalactiae was present in this study. The codon of Sip gene was optimized according to the Escherichia coli codon preference, and then the optimized gene was inserted into the expression vector pCzn1. Then, the newly constructed plasmid pCzn1-Sip was transfected into E. coli BL21 (Plys) cells for expression. Based on ultrasonication and purification by Ni column, the recombinant protein of Sip was obtained. The expression level and specificity of the recombinant codon optimized Sip were detected by SDS-PAGE and Western blot. The results showed that the 1 299 bp fragment of the optimized Sip gene was obtained by PCR amplification. The constructed recombinant plasmid pCzn1-Sip included 2 fragments about 4 400 bp and 1 299 bp after double digestion, which was consistent with the predicted value. The sequencing results showed that the optimized Sip gene was successfully transferred into the expression vector and the encoded amino acid sequence of Sip protein remained the same. SDS-PAGE and Western blot analysis showed that the recombinant Sip protein was obtained, which with a relative molecular weight of about 53 kD, and the recombinant optimized protein had S. agalactiae antigenicity. After purification by Ni column, it was found that the expression level of optimized soluble Sip was about 4 times compared with that of the non-optimized. Moreover, after immunization, the optimized Sip recombinant protein could supply about 69.23%~74.35% relative percent survivals against S. agalactiae challenge in tilapia. The results showed that the codon optimization of S. agalactiae surface protein Sip could obviously improve its expression level in E. coli. Moreover, the optimized Sip protein still has shown immunogenic. This study provides a scientific basis for the research and development of genetic engineering vaccines for tilapia streptococcus disease.
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