Enhancement of antigen-specific humoral immune responses and protein solubility through conjugation of bacterial flagellin, Vibrio vulnificus FlaB, to the N-terminus of porcine epidemic diarrhea virus surface protein antigen S0

Oh, Seo-ho; Kim Cho, Young-Saeng; Lee, Ho-Bin; Lee, Sang-Mok; Kim, Whee-Soo; Hong, Liang; Cho, Chong-Su; Choi, Yun-Jaie; Kang, Sang-Kee

As shown in Fig. 1A and C, and in our previous study [8] , the major fraction of S0 is expressed as an IB. In contrast to S0, 59% of S0-F was expressed as a soluble protein, while F-S0 was mainly expressed as an IB. Our data suggest that flagellin conjugation to the C-terminus of S0 improved solubility in the E. coli expression system without tig expression. To improve the solubility of the recombinant proteins, trigger factor chaperone tig, which has been shown to assist protein folding during synthesis and the initial folding process, was introduced and coexpressed with the respective protein of interest. In contrast to S0, which had 66% solubility, 99% of S0-F and F-S0 were expressed as soluble proteins ( Fig. 1B and D) , suggesting that flagellin conjugation also improved the solubility of recombinant proteins in the presence of tig. Furthermore, coexpression of tig ameliorated the solubility of S0, S0-F and F-S0 from 0% to 66%, 59% to 99%, and 6% to 99%, respectively. Taking this result into account, both flagellin conjugation and chaperone tig coexpression increased the solubility of S0-related recombinant proteins.