Structures of poliovirus complexes with anti-viral drugs: implications for viral stability and drug design

Picornaviruses, such as the structurally related polioviruses and rhinoviruses, are important human pathogens which have been the target of major drug development efforts. Receptor-mediated uncoating and thermal inactivation of poliovirus and rhinovirus are inhibited by agents that bind to each virus by inserting into a pocket in the beta barrel of the viral capsid protein, VP1. This pocket, which is normally empty in human rhinovirus-14 (HRV14), is occupied by an unknown natural ligand in poliovirus. Structural studies of HRV14-drug complexes have shown that drug binding causes large, localized changes in the conformation of VP1.

We report the crystal structures of six complexes between poliovirus and capsid-binding, antiviral drugs, including complexes of four different drugs with the Sabin vaccine strain of type 3 poliovirus, and complexes of one of these drugs with two other poliovirus strains that contain sequence differences in the drug-binding site. In each complex, the changes in capsid structure associated with drug binding are limited to minor adjustments in the conformations of a few side chains lining the binding site.

The minor structural changes caused by drug binding suggest a model of drug action in which it is the conformational changes prevented by the bound drug, rather than obvious conformational changes induced by drug binding, which exert the biological effect. Our results, along with additional structures of rhinovirus-drug complexes, suggest possible improvements in drug design, and provide important clues about the nature of the conformational changes that are involved in the uncoating process.