High-Resolution Structure Analysis of Antibody V5 and U4 Conformational Epitopes on Human Papillomavirus 16

Abstract

Cancers attributable to human papillomavirus (HPV) place a huge burden on the health of both men and women. The current commercial vaccines are genotype specific and provide little therapeutic benefit to patients with existing HPV infections. Identifying the conformational epitopes on the virus capsid supports the development of improved recombinant vaccines to maximize long-term protection against multiple types of HPV. Fragments of antibody (Fab) digested from the neutralizing monoclonal antibodies H16.V5 (V5) and H16.U4 (U4) were bound to HPV16 capsids and the structures of the two virus-Fab complexes were solved to near atomic resolution using cryo-electron microscopy. The structures reveal virus conformational changes, the Fab-binding mode to the capsid, the residues comprising the epitope and indicate a potential interaction of U4 with the minor structural protein, L2. Competition enzyme-linked immunosorbent assay (ELISA) showed V5 outcompetes U4 when added sequentially, demonstrating a steric interference even though the footprints do not overlap. Combined with our previously reported immunological and structural results, we propose that the virus may initiate host entry through an interaction between the icosahedral five-fold vertex of the capsid and receptors on the host cell. The highly detailed epitopes identified for the two antibodies provide a framework for continuing biochemical, genetic and biophysical studies.

RCSB Protein Data Bank tools for 3D structure-guided cancer research: human papillomavirus (HPV) case study

“…For HPV, a Molecule of the Month feature was recently presented, describing the connection to cancer and how an understanding of HPV proteins can help discover new ways to fight viral infection. A molecular origami foldable paper model of the HPV16 virus-like particle decorated with Fab fragments of the V5 antibody (PDB ID 6bt3 [ 37 ]) is downloadable as part of this outreach effort (Fig. 7 ).…”

“… Outreach materials include a feature and a foldable paper model of HPV (red) bound to antibody Fab fragments (blue) (PDB ID 6bt3 [ 37 ]*). …”

“…6 , which shows antibody-binding epitopes for two structures of HPV virus-like particles. Information from the primary reports for two PDB structures (PDB IDs 6bsp and 6bt3) of HPV16 with bound monoclonal antibodies U4 and V5, respectively, was used to define their epitopes [ 37 ], and then scripted for display using JSmol. U4 has a discontinuous epitope (red in Fig.…”

“… Epitopes (red) of antibodies U4 (left) and V5 (right) on HPV16 capsids, visualized with online JSmol scripting tools (PDB IDs 6bsp, 6bt3 [ 37 ]). …”

Structural characterization of a neutralizing mAb H16.001, a potent candidate for a common potency assay for various HPV16 VLPs

“…Interestingly, H16.001 and H16.8A9 reacted with all sorts of HPV16 VLPs comparably as manifested by almost overlapping binding response curves for five HPV16 VLP samples, indicating that H16.001 and H16.8A9 reactivities are tolerant and irrespective of the expression systems that generated the HPV16 VLPs, whereas H16.V5 reacted the best with E. coli-derived E1. 16 and worst with insect cell-derived I1.16. H16.4G12 bound with (Fig.…”