Arg85 is involved in the binding mechanism of the IL-4 super-agonist T13D and F82D. BIAcore sensorgrams of ligand-receptor interactions. Solutions of IL-4 variants (concentration 10 nM) were perfused over a sensor chip with immobilized IL4RαECD. (a) The variant IL4-T13D-R85A (green) shows a similar "fast" dissociation rate (k
off) as wild-type IL-4 (blue); the binding kinetics of the super-agonist IL4-T13D are shown in red for comparison. (b) As for T13DR85A, the variant F82DR85A (magenta) exhibits a fast dissociation rate compared to the super-agonistic single amino acid variant IL4-F82D (orange). However, the dissociation is even faster than wild-type IL4 (blue).