CPV purification and characterization. A. Sucrose gradient purification. VLPs preparation from infected cell culture lysates purified by sucrose gradient centrifugation (10–40%). Bands of CPV-VLPs that were derivatized with OG-488 are visible in the gradient just above the middle of the tube (left panel) and appear fluorescent green under a UV-light source (right panel). B. SDS-PAGE analyses. The purified VLPs were subjected to electrophoresis in 4–12% Bis-tris gel and stained with SimplyBlue (Invitrogen) to reveal the proteins (left panel). The Seeblue plus protein molecular weight standards in kDa (Invitrogen) are indicated on the side of the gel picture (lane 1). Lanes 2 and 3 contain protein from CPV-VLPs derivatized with OG-488 and CPV-VLPs respectively. Prior to staining, the gel (right panel) visualized with a UV-light source showed a fluorescent 62 kDa band in the lane of OG-488 derivatized CPV-VLPs (lane 2f) and lacked any fluorescent bands in the native CPV-VLPs (lane 3f).