Structure of human rhinovirus serotype 2 (HRV2)

Human rhinoviruses are classified into a major and a minor group based on their binding to ICAM-1 or to members of the LDL-receptor family, respectively. They can also be divided into groups A and B, according to their sensitivity towards a panel of antiviral compounds. The structure of human rhinovirus 2 (HRV2), which uses the LDL receptor for cell attachment and is included in antiviral group B, has been solved and refined at 2.6 A resolution by X-ray crystallography to gain information on the peculiarities of rhinoviruses, in particular from the minor receptor group. The main structural differences between HRV2 and other rhinoviruses, including the minor receptor group serotype HRV1A, are located at the internal protein shell surface and at the external antigenic sites. In the interior, the N termini of VP1 and VP4 form a three-stranded beta-sheet in an arrangement similar to that present in poliovirus, although myristate was not visible at the amino terminus of VP4 in the HRV2 structure. The betaE-betaF loop of VP2, a linear epitope within antigenic site B recognized by monoclonal antibody 8F5, adopts a conformation considerably different from that found in the complex of 8F5 with a synthetic peptide of the same sequence. This either points to considerable structural changes impinged on this loop upon antibody binding, or to the existence of more than one single conformation of the loop when the virus is in solution. The hydrophobic pocket of VP1 was found to be occupied by a pocket factor apparently identical with that present in the major receptor group virus HRV16. Electron density, consistent with the presence of a viral RNA fragment, is seen stacked against a conserved tryptophan residue.