Prediction on Antigenic Epitopes and Prokaryotic Expression of Imp Gene Encoding Immunodominant Membrane Protein from Lettuce Witches'-broom Phytoplasma

Immunodominant membrane protein gene (Imp) was amplified by PCR from the total DNA of diseased lettuce showing witches'-broom in Yuanmou County of Yunnan Province. The antigenic epitope of Imp was analyzed and the Imp gene was then expressed in prokaryotic cell. The result indicated that the Imp gene was 519 bp, encoding a protein of 172 amino acids. The molecular weight was 19 ku, the value of theoretical isoelectric point was 8.61. There was an obvious transmembrane area at the end of the N-terminal of Imp, but no signal peptide cleavage site. The prediction of Imp epitope showed that aa 62～83, aa 95～113, aa 113～145 should be the most possible epitope of Imp. The prokaryotic expression vector of pET30a-Imp was constructed and transformed into the host bacterium BL21(DE3)-plysS, and a fused protein of 25 ku was expressed by IPTG induction.