Abstract: The amino acid sequence of epitope peptides of the coat protein of strawberry mild yellow edge virus was predicted by bioinformatic tools including IEDB, DNAStar, DNAMAN and SnapGene. The peptide from the 27th to 38th amino acid residues with predicted high antigenic activity, referred to as AE, was reversely translated into its encoding DNA sequence according to the codon bias of E. coli. The encoding DNA fragment AE was then synthesized and cloned into the expression vector pET32a (+) between the EcoRⅠ and XhoⅠ sites. The open reading frame (ORF) containing the AE fragment was 561 bp, which encoded a fusion protein of 187 amino acid residues. The theoretical molecular mass of the recombinant fusion protein was 20.29 kD. Expression of the target gene in the recombinant plasmid pET32a (+)-AE was induced and optimized in E. coli BL21 (DE3) and E. coli Rosetta, respectively. The optimal expression conditions of the fusion protein in E. coli Rosetta were 1.5 mmol/L IPTG at 35 ℃ for 2 h, resulting in a yield of 13.22 mg/L, while those for expression in E. coli BL21(DE3) were 0.5 mmol/L IPTG at 30 ℃ for 2 h, giving a yield of 9.55 mg/L. The recombinant fusion protein was isolated by SDS-PAGE and identified by tandem mass spectrometry. The results showed that the recombinant fusion protein contained the designed peptide AE. The recombinant fusion protein was purified by Ni2+-affinity chromatography, digested by EK enzyme, and separated from the fusion protein tag by molecular sieve. Chicken immunoglobulin (IgY) was extracted from chicken eggs collected on the 21st day after the first injection. The binding activity of the IgY to AE and SMYEV was analyzed by the Dot-Blot method. The results showed that the IgY could specifically recognize both AE peptide and SMYEV indicating that the predicted AE peptide has desired immunogenicity.

Key words: strawberry mild yellow edge virus, coat protein, epitope prediction, prokaryotic expression, tandem mass spectrometry, immunogenicity