The analgesic domain of IL-2

Human recombinant interleukin-2 (IL-2) has been showed to exert an analgesic effect and some experiments suggested that opioid receptors were involved. Because the aromatic residues at the N-termini of opioid peptides are crucial for their binding to the opioid receptors, all nine aromatic residues in IL-2 were mutated by site-directed mutagenesis and both the analgesic activity and the immune activity of the wild-type and mutated IL-2 were tested. The result indicated that there exists a putative analgesic function domain in IL-2, in which Phe44, Tyr45, Tyr107, and Phe117 were essential. These four residues are located close together at the tertiary structure level of IL-2.