Quantitative characterization of the intrinsic ligand-binding affinity of the interleukin 2 receptor beta chain and its modulation by the alpha chain and a second affinity-modulating element.
The interleukin 2 receptor is a multisubunit receptor known to consist of at least two IL-2 binding subunits, alpha and beta. We report here kinetic evidence defining the contribution of an affinity-modulating element(s) intimately involved in modulation of the ligand-binding affinity of the beta chain and alpha/beta complex. The principal effect of this modulating element on the beta chain is to slow the dissociation of IL-2 more than 150-fold and thus raise its low intrinsic IL-2 binding affinity (Kd = 70 nM) as defined in transfected fibroblast cells to the level observed in lymphoid cells (Kd = 1.2 nM). The alpha subunit also increases the ligand-binding affinity of the beta chain, although in this case principally by increasing the association rate constant more than 1200-fold. The additional effect of the affinity-modulating element on the alpha/beta complex is minimal with regards to the equilibrium binding affinity. It does, however, have a detectable 14-fold effect on slowing the IL-2 dissociation rate. The existence of multiple forms of IL-2 receptor complexes with widely varying ligand affinities and dissociation rates illustrates the need for careful evaluation of binding data in studies of receptor subunit composition and reconstitution.
Ringheim
G E
GE
Central Research and Development, Glenolden Laboratory, DuPont, PA 19036.
Freimark
B D
BD
Robb
R J
RJ
D000818:Animals; D002460:Cell Line; D005784:Gene Amplification; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D046911:Macromolecular Substances; D011485:Protein Binding; D015375:Receptors, Interleukin-2 / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D007376:Interleukin-2; D008024:Ligands; D046911:Macromolecular Substances; D015375:Receptors, Interleukin-2; D011994:Recombinant Proteins