Expression and purification of chimeric peptide comprising EGFR B-cell epitope and measles virus fusion protein T-cell epitope in Escherichia coli

Abstract

Chimeric peptide MVF-EGFR237–267, comprising a B-cell epitope from the dimerization interface of human epidermal growth factor receptor (EGFR) and a promiscuous T-cell epitope from measles virus fusion protein (MVF), is a promising candidate antigen peptide for therapeutic vaccine. To establish a high-efficiency preparation process of this small peptide, the coding sequence was cloned into pET-21b and pET-32a respectively, to be expressed alone or in the form of fusion protein with thioredoxin (Trx) and His6-tag in Escherichia coli BL21 (DE3). The chimeric peptide failed to be expressed alone, but over-expressed in the fusion form, which presented as soluble protein and took up more than 30% of total proteins of host cells. The fusion protein was seriously degraded during the cell disruption, in which endogenous metalloproteinase played a key role. Degradation of target peptide was inhibited by combined application of EDTA in the cell disruption buffer and a step of Source 30Q anion exchange chromatography (AEC) before metal-chelating chromatography (MCAC) for purifying His6-tagged fusion protein. The chimeric peptide was recovered from the purified fusion protein by enterokinase digestion at a yield of 3.0mg/L bacteria culture with a purity of more than 95%. Immunogenicity analysis showed that the recombinant chimeric peptide was able to arouse more than 1×104 titers of specific antibody in BALB/c mice. Present work laid a solid foundation for the development of therapeutic peptide vaccine targeting EGFR dimerization and provided a convenient and low-cost preparation method for small peptides.