HIGH-RESOLUTION STRUCTURE OF A POLYOMAVIRUS VP1-OLIGOSACCHARIDE COMPLEX - IMPLICATIONS FOR ASSEMBLY AND RECEPTOR-BINDING

The crystal structure of a recombinant polyomavirus VP1 pentamer (resi dues 32-320) in complex with a branched disialylated hexasaccharide re ceptor fragment has been determined at 1.9 Angstrom resolution, The re sult extends our understanding of oligosaccharide receptor recognition , It also suggests a mechanism for enhancing the fidelity of virus ass embly, We have previously described the structure of the complete poly omavirus particle complexed with this receptor fragment at 3.65 Angstr om, The model presented here offers a much more refined view of the in teractions that determine carbohydrate recognition and allows us to as sign additional specific contacts, in particular those involving the ( alpha 2,6)-linked, branching sialic acid, The structure of the unligan ded VP1 pentamer, determined independently, shows that the oligosaccha ride fits into a preformed groove and induces no measurable structural rearrangements, A comparison with assembled VP1 in the virus capsid r eveals a rearrangement of residues 32-45 at the base of the pentamer. This segment may help prevent the formation of incorrectly assembled p articles by reducing the likelihood that the C-terminal arm will fold back into its pentamer of origin.