Solution Assembly of the Pseudo-high Affinity and Intermediate Affinity Interleukin-2 Receptor Complexes

The high affinity interleukin‐2 receptor is composed of three cell surface subunits, IL‐2Rα, IL‐2Rβ, and IL‐2Rγ. Functional forms of the IL‐2 receptor exist, however, that enlist only two of the three subunits. On activated T‐cells, the α‐ and β‐subunits combine as a preformed heterodimer (the pseudo‐high affinity receptor) that serves to capture IL‐2. On a subpopulation of natural killer cells, the β‐ and γ‐subunits interact in a ligand‐dependent manner to form the intermediate affinity receptor site. Previously, we have demonstrated the feasibility of employing coiled‐coil molecular recognition for the solution assembly of a heteromeric IL‐2 receptor complex. In that study, although the receptor was functional, the coiled‐coil complex was a trimer rather than the desired heterodimer. We have now redesigned the hydrophobic heptad sequences of the coiled‐coils to generate soluble forms of both the pseudo‐high affinity and the intermediate affinity heterodimeric IL‐2 receptors. The properties of these complexes were examined and their relevance to the physiological IL‐2 receptor mechanism is discussed