Effects of IL-1 receptor accessory protein on IL-1 binding

Interleukin-l (IL-I) is an important pro-inflammatory cytokine that exerts its diverse biological functions bg binding to a receptor complex consisting of two transmembrane proteins, type I IL-l receptor (IL-1RI) and IL-1 receptor accessory protein (IL-IRAcP). Both receptor chains are indispensable for IL-l signaling, hut only IL-IRI is able to bind the cytokine, The effects of IL-1RAcP on IL-l binding are unclear. This study shows that although expression of IL-1RAcP does not alter the equilibrium dissociation constant of IL-1, it has an effect on the non-equilibrium binding modus, most likely due to changes in on/off rates. This defines an additional function of IL-1RAcP: it stabilizes the active IL-I receptor complex. (C) 1998 Federation of European Biochemical Societies.