Cyclic disulfide model of the major antigenic site of serotype‐C foot‐and‐mouth disease virus

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Abstract
A cyclic disulfide peptide representing antigenic site A of foot‐and‐mouth‐disease virus (FMDV) strain C‐S8cl (residues 134 to 155 of viral protein l (VP1) with Tyr136 and Arg153 replaced by cystine; TTCTASARGDLAHLTTTHACHL) was synthesized by solid phase methods. Formation of the cyclic disulfide was carried out by air oxidation of the fully deprotected and reduced bis‐cysteine precursor, under high dilution conditions. The identity of the cyclic peptide was confirmed by both physical and enzymatic methods. A conformational study of the cyclic peptide and of its linear parent structure (YTASARGDLAHLTTTHARHLP, residues 136–156 of VP1 of FMDV C‐S8cl) by circular dichroism in the presence of a structure‐inducing solvent showed the cyclic disulfide analog to adopt lower levels of α‐helix than its linear counterpart. In competitive ELISA assays both peptides reacted with similar affinity against a representative panel of neutralizing monoclonal antibodies directed towards antigenic site A. Thus, a high inherent flexibility of this loop may preclude a conformational restriction strong enough to alter recognition by anti‐virus antibodies.