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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 A [R = 0.16 for
reflections with F greater than 3 sigma(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 beta-barrel
moieties. VP4 is associated with the capsid interior by a distributed network of
contacts with VP1, VP2 and VP3 within a promoter. 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 beta C, beta H, beta E and beta F strands of VP3 in one pentamer and beta
A1 and beta A2 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 beta-barrels of human rhinovirus
14 VP1, VP2 and VP3 are compared with each other and with the southern bean
mosaic virus coat protein.
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