Antigenic epitopes of PEDV S protein in Chinese strains
Five major neutralizing epitopes S1A (435–485aa), COE domain(499–638 aa), SS2 (748–755aa), SS6(764–771aa), 2C10(1368–1374aa), and one linear B-cell epitope (SE16, 722–731aa) have been identified on the surface of S protein. Among these epitopes, SS2, 2C10 and SE16 (data not shown) domain of all field PEDVs were highly conserved, with only one mutation (1374Y-C) in the 2C10 as compared to the two vaccine strains. The aa difference was compared among field strains and vaccine strain CV777 and AJ1102. All of the field strains had two aa substitutions (764L-S/Por 766D-S/F ). One mutation 765Q-Hin the epitope SS6 of CH/GXLZ/202010 was observed. In the S1A epitope, the field strains except for CH/GXLZ/202010 and CH/HNSQ/202102 had one mutation (479S-A). In the COE domain, all field strains except for CH/HNSQ/202102 had three substitutions (552T-S, 597G-S and 636Q-E/R). Meanwhile, a serine substitution (520A-S) was observed in all field strains except for CH/HNXX/202011, CH/JSSQ/202010 and CH/SCCN/202008. In addition, multiple mutations on S protein were detected in the COE domain (499I-T, 502V-I, 524H-S/L/Y, 539F-L, 566K-N, 569D-A/N, 606Y-H, 612G-V/S and 634P-S) (Figure 4) .