Binding of knob-specific DARPins to virion-associated fibers. DARPins F4 (filled bars) and 2E6 (open bars), immobilized via their biotinylated AviTag to a streptavidin-coated ELISA plate, were probed with the particles of Ad vectors (Ad5lucΔF, fiber-depleted virus; Ad5Luc1, virus containing the wild-type knob; Ad5LucFΔ-TAYT, virus containing the knob with a 4 bp deletion in the FG loop of the knob) shown below the graph. DARPin-bound Ads were detected with an anti-Ad antibody and HRP-labeled secondary antibody. Background determined in casein-coated wells was at an absorbance at 490 nm (A490) of 0.2 and has not been subtracted. Error bars show standard deviation calculated for triplicate data points.