Analysis of Potato virus Y Coat Protein Epitopes Recognized by Three Commercial Monoclonal Antibodies

BACKGROUND: Potato virus Y (PVY, genus Potyvirus) causes substantial economic losses in solanaceous plants. Routine screening for PVY is an essential part of seed potato certification, and serological assays are often used. The commercial, commonly used monoclonal antibodies, MAb1128, MAb1129, and MAb1130, recognize the viral coat protein (CP) of PVY and distinguish PVY(N) strains from PVY(O) and PVY(C) strains, or detect all PVY strains, respectively. However, the minimal epitopes recognized by these antibodies have not been identified. METHODOLOGY/PRINCIPAL FINDINGS: SPOT peptide array was used to map the epitopes in CP recognized by MAb1128, MAb1129, and MAb1130. Then alanine replacement as well as N- and C-terminal deletion analysis of the identified peptide epitopes was done to determine critical amino acids for antibody recognition and the respective minimal epitopes. The epitopes of all antibodies were located within the 30 N-terminal-most residues. The minimal epitope of MAb1128 was (25)NLNKEK(30). Replacement of (25)N or (27)N with alanine weakened the recognition by MAb1128, and replacement of (26)L, (29)E, or (30)K nearly precluded recognition. The minimal epitope for MAb1129 was (16)RPEQGSIQSNP(26) and the most critical residues for recognition were (22)I and (23)Q. The epitope of MAb1130 was defined by residues (5)IDAGGS(10). Mutation of residue (6)D abrogated and mutation of (9)G strongly reduced recognition of the peptide by MAb1130. Amino acid sequence alignment demonstrated that these epitopes are relatively conserved among PVY strains. Finally, recombinant CPs were produced to demonstrate that mutations in the variable positions of the epitope regions can affect detection with the MAbs. CONCLUSIONS/SIGNIFICANCE: The epitope data acquired can be compared with data on PVY CP-encoding sequences produced by laboratories worldwide and utilized to monitor how widely the new variants of PVY can be detected with current seed potato certification schemes or during the inspection of imported seed potatoes as conducted with these MAbs.