The crystal structure of coxsackievirus A9: new insights into the uncoating mechanisms of enteroviruses.

Coxsackievirus A9 (CAV9), a human pathogen causing symptoms ranging from common colds to fatal infections of the central nervous system, is an icosahedral single-stranded RNA virus that belongs to the genus Enterovirus of the family Picornaviridae. One of the four capsid proteins, VP1, includes the arginine-glycine-aspartate (RGD) motif within its C-terminal extension. This region binds to integrin alpha v beta 3, the only receptor for CAV9 to be conclusively identified to date. The crystal structure of CAV9 in complex with the antiviral compound WIN 51711 has been solved to 2.9 A resolution. The structures of the four capsid proteins, VP1 to VP4, resemble those of other picornaviruses. The antiviral compound is bound in the VP1 hydrophobic pocket, and it is possible that the pocket entrance contains a second WIN 51711 molecule. Continuous electron density for the VP1 N terminus provides a complete picture of the structure close to the fivefold axis. The VP1 C-terminal portion is on the outer surface of the virus and becomes disordered five-residues N-terminal to the RGD motif. The RGD motif is exposed and flexible in common with other known integrin ligands. Although CAV9 resembles coxsackie B viruses (CBVs), several substitutions in the areas implicated in CBV receptor attachment suggest it may recognise a different receptor. The structure along the fivefold axis provides new information on the uncoating mechanism of enteroviruses. CAV9 might bind a larger natural pocket factor than other picornaviruses, an observation of particular relevance to the design of new antiviral compounds.