Abstract
Human rhinovirus 14 has a pseudo T = 3 icosahedral structure in which 60 copies of the three larger capsid proteins VP1, VP2 and VP3 are arranged in an icosahedral surface lattice, reminiscent of T = 3 viruses such as tomato bushy stunt virus and southern bean mosaic virus. The overall secondary and tertiary structures of VP1, VP2 and VP3 are very similar. The structure of human rhinovirus 14, which was refined at a resolution of 3.0 Å [R = 0.16 for reflections with F > 3σ(F)], is here analyzed in detail.
Quantitative analysis of the surface areas of contact (proportional to hydrophobic free energy of association) supports the previously assigned arrangement within the promoter, in which interactions between VP1 and VP3 predominate. Major contacts among VP1, VP2 and VP3 are between the β-barrel moieties. VP4 is associated with the capsid interior by a distributed network of contacts with VP1, VP2 and VP3 within a protomer. As the virion assembly proceeds, the solvent-accessible surface area becomes increasingly hydrophilic in character. A mixed parallel and antiparallel seven-stranded sheet is composed of the βC, βH, βE and βF strands of VP3 in one pentamer and βA1 and βA2 of VP2 and the VP1 amino terminus in another pentamer. This association plays an essential role in holding pentamers together in the mature virion as this contact region includes more than half of the total short non-bonded contacts between pentamers. Contacts between protomers within pentamers are more extensive than the contacts between pentamers, accounting in part for the stability of pentamers.
The previously identified immunogenic regions are correlated with high solvent accessibility, accessibility to large probes and also high thermal parameters. Surface residues in the canyon, the putative cellular receptor recognition site, have lower thermal parameters than other portions of the human rhinovirus 14 surface. Many of the water molecules in the ordered solvent model are located at subunit interfaces. A number of unusual crevices exist in the protein shell of human rhinovirus 14, including the hydrophobic pocket in VP1 which is the locus of binding for the WIN antiviral agents. These may be required for conformational flexibility during assembly and disassembly. The structures of the β-barrels of human rhinovirus 14 VP1, VP2 and VP3 are compared with each other and with the southern bean mosaic virus coat protein.