Soluble production of a full-length human papillomavirus type 16 L1 protein by Escherichia coli

Persistent infection with human papillomavirus type 16 (HPV16) causes the development of cervical cancer. Escherichia coli is a cost-effective host successfully used to develop a second-generation vaccine against HPV, based on the purification of soluble truncated L1 protein variants. Previous attempts to produce soluble full-length HPV16-L1 protein by E. coli have failed. This study was aimed at cloning a Cuban HPV16-L1 gene in E. coli and assessing its expression as a soluble full-length L1 protein by manipulating culture conditions. The L1 gene was amplified from a Cuban patient’s cervical sample and cloned into pET28a and pBAD/Myc-HisA vectors. Production and solubility of L1 protein were evaluated in E. coli TOP10 harboring pBADHPV16-L1 plasmid and E. coli BL21-(DE3), Rosetta-(DE3)/pLysS, and SHuffle® T7 Express lysY strains harboring pETHPV16-L1 plasmid, grown under arabinose (0.2%)- or isopropyl β-D-1-thiogalactopyranoside (IPTG, 100 µM)-induction or Super Broth-based auto-induction for 24 and 48 h. The recombinant plasmids pETHPV16-L1 and pBADHPV16-L1 were constructed. The HPV16-L1 protein was produced insoluble to high levels in conventionally IPTG-induced E. coli-pETHPV16-L1 cells. However, under auto-induction, soluble full-length HPV16-L1 protein was successfully produced at similar levels by E. coli BL21 (DE3), Rosetta (DE3) pLysS and SHuffle® T7 Express lysY cells, reaching up to 7.2 ± 0.5% and 14.3 ± 1.6% of the total proteins in the soluble fraction after growing for 24 and 48 h, respectively. It is concluded that the auto-induction procedure at 18 °C with 30 µM IPTG and 100 rev/min promotes soluble full-length HPV16-L1 protein production by E. coli.