Papillomavirus capsid protein expression in Escherichia coli: Purificationand assembly of HPV11 and HPV16 L1

The L1 major capsid proteins of human papillomavirus (HPV) types 11 and 16 were purified and analyzed for structural integrity and in vitro self-assem bly. Proteins were expressed in Escherichia coli as glutathione-S-transfera se (GST-L1) fusions and purified to near homogeneity as pen tamers (equival ent to viral capsomeres), after thrombin cleavage from the GST moiety and r emoval of tightly associated GroEL protein. Sequences at the amino and carb oxy termini contributing to formation of L1 pentamers and to in vitro capsi d assembly were identified by deletion analysis. For both HPV11 and HPV16 L 1, up to at least ten residues could be deleted from the amino terminus (De lta N10) and 30 residues from the carboxy terminus (Delta C30) without affe cting pentamer formation. The HPV16 pentamers assembled into relatively reg ular, 72-pentamer shells ("virus-like particles" or VLPs) at low pH, with t he exception of HPV16 L1 Delta N10, which assembled into a 12-pentamer, T = 1 capsid (small VLP) under all conditions tested. The production of large quantities of assembly-competent L1, using the expression and purification protocol described here, has been useful for crystallographic analysis, and will be valuable for studies of virus-receptor interactions and potentiall y for vaccine design. (C) 2001 Academic Press.