An HBGA binding assay [8, 18] was used to test the functionality of the purified VLPs as well as to determine the significance of the conformational binding sites on the VLP, which would presumable require intact VLPs. A comparison of the binding of VLPs purified by sucrose gradient centrifugation and by CsCl sedimentation, as well as heat-treated VLPs (60°C, 1 h), to synthetic biotinylated H type 3 carbohydrate is shown in Fig. 3 . The binding was clearly dependent on the morphology and preserved structure of the VLPs, with the lowest level of binding observed with the heat-treated VLPs with disrupted conformational binding sites. Lewis b antigen was used as a control in the assay, and this did not bind to any of the VLPs (Fig. 3) .