Refolding and purification of human papillomavirus type 16 E7-lacZ fusion protein expressed in Escherichia coli

Expression and purification of His-tagged HPV16 E7 protein active in pRb binding

Human papillomavirus type 16 (HPV16) protein E7 is the major oncogenic factor associated with the development of human cervical cancer. The transforming activity of the E7 protein is linked to its interaction with host regulatory proteins such as the retinoblastoma tumor suppressor protein. The recombinant production of E7 protein is a prerequisite for its structural and functional characterization as well as for the development of various preventive and therapeutic strategies. We present an approach to enhance the soluble expression of His-tagged E7 protein by optimization of the E7 gene and the expression conditions in the host Escherichia coli. We also report a detailed protocol for the purification of E7 protein by standard chromatographic methods. The binding of E7 protein to the recombinant non-phosphorylated form of retinoblastoma protein was examined by ELISA and surface plasmon resonance analysis. These studies confirm that the recombinant His-tagged E7 protein retains its conformational properties and biological activity.

Expression, purification and immunological characterization of the transforming protein E7, from cervical cancer-associated human papillomavirus type 16

E7 is the major oncogenic protein produced in cervical cancer-associated human papillomavirus type 16 (HPV16). This protein was expressed in Escherichia coli as a glutathione-S-transferase (GST) fusion protein. E7-enriched inclusion bodies were collected from bacterial lysates, were solubilized in 10 M urea, and the protein was purified using anion exchange column chromatography. After removal of endotoxin with serial Triton X-114 extractions, material of high purity (about 90%) was obtained, which is suitable for use in a human clinical trial. This material was immunogenic, and when used as a vaccine, protected mice against challenge with an HPV16 E7 DNA transfected tumour cell line. Based on this observation, the E7GST fusion protein is currently being used in a human clinical trial of a vaccine against HPV16-induced cervical cancer. This fusion protein could be cleaved with thrombin to remove the GST fusion part and further purified by preparative SDS gel electrophoresis to obtain free E7 with > 98% purity.

A general purification protocol for E7 proteins from "high- and low-risk" human papillomavirus types expressed in the yeast Schizosaccharomyces pombe

A purification protocol was developed to obtain human papillomavirus (HPV) type 16 E7 protein expressed in the yeast Schizosaccharomyces pombe. Only three chromatographic steps were necessary to purify the unfused HPV 16 E7 protein to homogeneity (95-99%) as shown by silver staining after polyacrylamide gel electrophoresis. Approximately 0.8 mg of highly purified E7 was obtained from 5 x 10(10) yeast cells. The purified HPV 16 E7 phosphoprotein (Ser 31/32) was refolded and assayed for functionality. Binding to the proteins Rb1 and p107 in vitro and induction of DNA synthesis after microinjection into serum-deprived NIH 3T3 cells suggest that the E7 protein retains some of its biological activities. Most importantly, the purification strategy is also applicable for different HPV 16 E7 mutants and for E7 proteins from other HPV types such as HPV 18 and 11.

Nucleic acid binding by zinc finger-like motif of human papillomavirus type 16 E7 oncoprotein

Human papillomavirus (HPV) types 16 and 6b E7 proteins and their chimeric or mutant proteins were analyzed for oligonucleotide-binding activity by surface plasmon resonance-based biomolecular interaction analysis. The results indicated that type 16 E7 protein has stronger nucleic acid-binding activity than that of type 6b E7 protein. In addition, the results also indicated that the zinc finger-like motif in the C-terminal region of the type 16 E7 protein plays an important role in this activity.