Foot-and-mouth disease virus: immunogenicity and structure of fragments derived from capsid protein VP and of virus containing cleaved VP.

Peptide fragments were obtained from the immunogenic capsid protein VP3, ca. 24 kilodaltons (kd), of foot-and-mouth disease virus type A12 119ab by three procedures: (1) spontaneous proteolysis of in virion VP3 in tissue cultures to produce a 15 kd peptide, designated S fragment; (2) trypsin treatment of purified virus to produce a 16 kg peptide, designated T fragment; and (3) cyanogen bromide cleavage of purified VP3 to produce a 13 kd fragment. Following isolation and purification by gel electrophoresis, VP3 and each of the three fragments were immunogenic for livestock. Lyophilization appeared to impair the immunogenicity of VP3. In addition, viruses containing VP3 fragments produced either by the spontaneous- or trypsin-induced proteolysis were as immunogenic as virus with its VP3 intact. Amino acid sequencing of N-terminal regions revealed that the S fragment was homologous with the N-terminus of VP3, whereas the 13 kd fragment possessed a unique N-terminus. Thus, putative common immunogenic amino acid sequences would appear to reside within an overlap region of the 15 kd S and 13 kd fragments. Sequencing of cDNA prepared to viral genome RNA provided three kinds of information: it (1) placed the above overlap region in the second and third quarters of VP3; (2) demonstrated that the codons for the C-terminus of VP1 and N-terminus of VP3 are contiguous; and (3) supported earlier evidence that these same codons program a chain reversal where VP1 and VP3 are joined in the precursor polyprotein.