Identification of conformational epitopes and antigen-specific residues at the D/A domains and the extramembrane C-terminal region of E2 glycoprotein of classical swine fever virus
2012
Chang, Chia-Yi | Huang, Chin-Cheng | Deng, Ming-Chung | Huang, Yeou-Liang | Lin, Yuru | Liu, Hsin-Meng | Lin, Yeou-Liang | Wang, Fun-In
Envelope glycoprotein E2 of classical swine fever virus (CSFV) is the major antigen that induces neutralizing antibodies in infected pigs. Previous studies revealed that both conformation-dependent and linear epitopes are most present within domains B/C/D/A in the N-terminal half of E2. However, studies of antigenicity beyond the B/C domains remain limited. This study revealed that conformational epitopes were present on the D/A domains as well as the proximal C-terminal of E2, since the mutation of cysteine abrogated their bindings to monoclonal antibodies (mAbs). The residue R845 at domain A and E902 at the C-terminal region were critical for specific binding to mAbs, further supporting the presence of antigenic determinants on these regions. Substitutions of cysteines in domains D/A not only abrogated the binding to mAbs directed to D/A, but also affected the binding of the downstream C-terminal region to its specific mAbs, suggesting a close interaction between the two conformational epitopes. Mutations on the five proximal cysteines at positions 869, 877, 893, 896 and 930 in the C-terminal region only affected the binding to its specific mAbs binding sites. In addition, mutation on the three distal C-terminal cysteines at positions 945, 966, and 983 resulted in loss of E2 homodimerization. This study demonstrates new antigenic epitopes on D/A domains and C-terminal of E2 that have not been reported before, and that the nine cysteines in the C-terminal function differently in either maintaining the antigenic structure or in intermolecular dimerization of E2.
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