Biochemical evidence for a third chain of the interleukin-2 receptor.
Two receptor proteins that specifically bind interleukin-2 (IL-2) have been identified previously. The L (Tac or alpha) chain can bind IL-2 with a Kd value of 10 nM (low affinity). Although the H (beta) chain expressed on lymphocytes can bind IL-2 with a Kd value of 1 nM (intermediate affinity), transfected fibroblasts expressing the H chain cannot bind IL-2, suggesting the involvement of other lymphocyte-specific factors for the function of the H chain. To obtain direct evidence for the presence of a third component of the IL-2 receptor, we examined the IL-2 binding activity of detergent-solubilized cell membrane preparations. We found that lysates of transfected Cos7 cells expressing H chains can bind IL-2 when mixed with lysates from lymphocytes that cannot bind IL-2. Chemical cross-linking of 125I-IL-2-bound lysate mixture and subsequent immunoprecipitation with a noncompetitive anti-H chain antibody gave rise to two 125I-IL-2-bound proteins, a 56-kDa protein (p56) and the H chain, although neither the H chain nor p56 alone is able to bind IL-2. These results indicate that p56 is the IL-2 receptor third chain that is required for IL-2 binding to the H chain. A similar lysate mixing experiment also showed that p56 is involved in IL-2 binding to the high affinity IL-2 receptor by forming the quaternary complex of IL-2, p56, L chain, and H chain.
Department of Medical Chemistry Faculty of Medicine, Kyoto University, Japan.
Y
Y
Saito
H
H
Tada
H
H
Sabe
T
T
Honjo
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D015723:Gene Library; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism; D007700:Kinetics; D008214:Lymphocytes / Q000276:immunology; D046911:Macromolecular Substances; D008970:Molecular Weight; D011485:Protein Binding; D015375:Receptors, Interleukin-2 / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D014162:Transfection
D007376:Interleukin-2; D046911:Macromolecular Substances; D015375:Receptors, Interleukin-2