title: The structure of the interleukin-15 alpha receptor and its implications for ligand binding.
abstract: Interleukin (IL)-15 is a member of the small four alpha-helix bundle family of cytokines. IL-15 was discovered by its ability to mimic IL-2-mediated T-cell proliferation. Both cytokines share the beta and gamma receptor chains of the IL-2 receptor for signal transduction. However, in addition, they target specific alpha chain receptors IL-15Ralpha and IL-2Ralpha, respectively. The exceptionally high affinity binding of IL-15 to IL-15Ralpha is mediated by its sushi domain. Here we present the solution structure of the IL-15Ralpha sushi domain solved by NMR spectroscopy and a model of its complex with IL-15. The model shows that, rather than the familiar hydrophobic forces dominating the interaction interface between cytokines and their cognate receptors, the interaction between the IL-15 and IL-15Ralpha complex involves a large network of ionic interactions. This type of interaction explains the exceptionally high affinity of the IL-15.IL-15Ralpha complex, which is essential for the biological effects of this important cytokine and which is not observed in other cytokine/cytokine receptor complexes.
authors.affiliation: Biochemisches Institut der Christian-Albrechts-Universität Kiel, Olshausenstrasse 40, 24118 Kiel, Germany.
authors.forename: Inken
authors.initials: I
authors.lastname: Lorenzen
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Dingley
authors.forename: Yannick
authors.initials: Y
authors.lastname: Jacques
authors.forename: Joachim
authors.initials: J
authors.lastname: Grötzinger
mesh_terms: D018360:Crystallography, X-Ray; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007376:Interleukin-2 / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D040681:Structural Homology, Protein
chemical_list: C508024:IL15RA protein, human; D007376:Interleukin-2; D008024:Ligands; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2