N-terminal Domain of the Spike Protein of Porcine Epidemic Diarrhea Virus as a New Candidate Molecule for a Mucosal Vaccine

Kim, Sae-Hae; Cho, Byeol-Hee; Lee, Kyung-Yeol; Jang, Yong-Suk

The prototype Belgian CV777 strain (genogroup 1) of PEDV was first identified in 1978 (2) . The genomic sequence of the currently prevalent PEDV strain spreading rapidly in South Korea, the United States, and China differs from that of the CV777 strain (18) . The BM1 strain of PEDV isolated from South Korea during October 2013 to June 2014 belongs to subgroup 2a, genogroup 2 of PEDV, and its genomic sequence is 99.2% similar to those of North American strains of PEDV (19) . The S gene of PEDV BM1 strain consists of the S1 region (residues 21-793) encoding the receptor-binding domain and the S2 region (residues 794-1385), involved in viral fusion to host cells. The S1 region in the PEDV BM1 strain consists of an NTD (residues 231-501) with sugar-binding ability and a CTD (residues 502-780) containing a pAPN-binding site (Fig. 1) . Previous studies have suggested that the NTD has sugar-binding ability and aids in host receptor binding of PEDV (8) . However, the role of the domain as a mucosal vaccine Ag has been poorly studied. We first attempted to express recombinant NTD 231-501 of the PEDV S1 protein and constructed pGEX 4T-1 encoding the NTD 231-501 gene with an N-terminal GST tag ( Fig. 2A) . Recombinant NTD 231-501 of the PEDV S1 protein was produced in E. coli, and western blot analysis of the bacterial cell lysate using the anti-GST Ab revealed a specific 55 kDa band (Fig. 2B) . The soluble fraction of recombinant NTD 231-501 protein was purified by glutathione Sepharose chromatography (Fig. 2C) .