Subunit interactions in bovine papillomavirus

Abstract

Papillomaviruses, members of a group of dsDNA viruses associated with epithelial growths and tumors, have compact capsids assembled from 72 pentamers of the protein L1. We have determined the structure of bovine papillomavirus by electron cryomicrosopy (cryoEM), at ∼3.6 Å resolution. The density map, obtained from single-particle analysis of ∼4,000 particle images, shows the trace of the L1 polypeptide chain and reveals how the N-and C-terminal "arms" of a subunit (extensions from its β-jelly-roll core) associate with a neighboring pentamer. Critical contacts come from the C-terminal arm, which loops out from the core of the subunit, forms contacts (including a disulfide) with two subunits in a neighboring pentamer, and reinserts into the pentamer from which it emanates. This trace corrects one feature of an earlier model. We discuss implications of the structure for virion assembly and for pathways of infectious viral entry. We suggest that it should be possible to obtain image reconstructions of comparable resolution from cryoEM images of asymmetric particles. From the work on papillomavirus described here, we estimate that such a reconstruction will require about 1.5 million images to achieve the same number of averaged asymmetric units; structural variability will increase this number substantially. virus assembly | virus structure | icosahedral symmetry

Kallikrein-8 Proteolytically Processes Human Papillomaviruses in the Extracellular Space To Facilitate Entry into Host Cells

“…A cleavage at the C-terminal site 417R would generate pentamers that would be no longer covalently linked by the invading C-terminal arm's disulfide bond (between residues C175 and C428) (8,76,77) potentially generating a particle that is primed for uncoating by cyclophilins in the endosomal pathway. With a calculated size of 9.7 kDa, however, the cleaved peptide may be too large to account for our experimental results.…”

“…Particle stability is achieved by extensive hydrophobic interactions between the five L1 molecules forming the capsomers. The capsomers are linked by the invading C-terminal arm of an L1 molecule from a neighboring capsomer (7,8). In addition, papillomaviruses undergo, like many other viruses, a maturation process after initial assembly.…”

Characterization of virus-like particles in GARDASIL® by cryo transmission electron microscopy

“…2D), and it also appears that the antibody binds to the capsomers at the located 3-fold axes of symmetry, and not to those located at the 5-fold axes of symmetry,, possibly due to a more restricted spacing between capsomers at the 5-fold axis as compared with those at the 3-fold axis. 17 From these 3D maps, we deduce that there are 300 potential binding sites on the H16 serotype for the H16.V5 antibody.…”

The U4 Antibody Epitope on Human Papillomavirus 16 Identified by Cryo-electron Microscopy

“…Twelve capsomers lie on an icosahedral five-fold vertex and are referred to as pentavalent capsomers, whereas the remaining 60 capsomers are each surrounded by six other capsomers and referred to as hexavalent capsomers. The C terminus of each L1 protein, called the C-terminal arm, extends along the capsid floor to interact with the neighboring capsomer before returning to the original donor cap-somer (9,17,18). Intercapsomer disulfide bonds are formed between cysteine C428 and C175, which stabilize the icosahedral structure and play an important role in virus maturation (18,19).…”