Probing the Binding of Interleukin-23 to Individual Receptor Components and the IL23 Heteromeric Receptor Complex in Living Cells Using NanoBRET

Interleukin-23 (IL23) is a pro-inflammatory cytokine involved in the host defence against pathogens, but also implicated in the development of several autoimmune disorders. The IL23 receptor has become a key target for drug discovery but the exact mechanism of the receptor ligand interaction remains poorly understood. In this study the affinities of IL23 for its individual receptor components (IL23R and IL12Rβ1) and the heteromeric complex formed between them have been measured in living cells using NanoLuciferase tagged full-length proteins. Here, we demonstrate that TAMRA-tagged IL23 has a greater than seven fold higher affinity for IL12Rβ1 than IL23R. However, in the presence of both receptor subunits IL23 affinity is increased more than three orders of magnitude to 27 pM. Furthermore, we show that IL23 induces a potent change in the position of the N -terminal domains of the two receptor subunits consistent with a conformational change in the heteromeric receptor structure.