E6 protein of human papillomavirus 16 (HPV16) expressed in Escherichia coli sans a stretch of hydrophobic amino acids, enables purification of GST-ΔE6 in the soluble form and retains the binding ability to p53

Recombinant E6 expressed in Escherichia coli is known to form recalcitrant inclusion bodies even when fused to the soluble GST protein. This study describes the modification of the HPV genotype-16 oncogenic protein E6 in order to obtain it in the soluble form. The modified protein (ΔE6) was expressed in E. coli BL21 as an N-terminal fusion with GST (GST-ΔE6). ΔE6 was constructed by deleting the nucleotide sequences coding for IHDIIL (31-36 a.a), one of the highly hydrophobic peptide stretches, using splicing by overextension polymerase chain reaction (SOE-PCR). The removal of IHDIIL residues rendered the GST-ΔE6 soluble and amenable for purification involving a two step process a preliminary glutathione-GST affinity chromatography followed by gel-filtration chromatography. Evaluation of purified protein fractions by HPLC suggests that GST-ΔE6 exists as a monomer. Further, the ΔE6 in GST-ΔE6 seemed to retain the binding ability to p53 as determined by the glutathione-GST capture ELISA. Purified GST-ΔE6 we reckon, might find use as an essential reagent in immunological assays, in sero-epidemiological studies, and also in studies to delineate the structure and function of HPV16 E6.