A novel human papillomavirus type 6 neutralizing domain comprising two discrete regions of the major capsid protein L1

We have mapped the binding sites on human papillomavirus (HPV) type 6 for t hree HPV 6-specific neutralizing monoclonal antibodies (mAbs). The critical binding residues were first identified by making HPV 11-like amino acid su bstitutions in the HPV 6 major capsid protein L1 and assaying the resulting virus-like particles (VLPs) for reactivity with the mAbs. To confirm the r elevance of these residues for mAb binding, we demonstrated that HPV 6 type -specificity could be transferred to HPV 11 VLPs by making the appropriate HPV 6-like amino acid substitutions in the HPV 11 L1. Two binding regions w ere found. For one mAb, all critical residues are centered at residue 53, w hile for the other two mAbs, type-specific binding also requires a second s ite located more than 100 residues distal to the first. Both binding sites coincide with regions of Ll where the sequences of the closely related HPV 6 and 11 diverge. These regions are where the Ll sequences are the least we ll conserved among all HPV types and they have been implicated in type-spec ific binding for other HPV types. This suggests that clusters of diverged r esidues, surrounded by conserved Ll sequences, are presented on the surface of assembled particles and are responsible for eliciting critical humoral immune responses to the virus. (C) 2001 Academic Press.