Fig. 5: Conformational heterogeneity of hIL-1β maps to the binding site of (S)-2.

a Superposition of the hIL-1β/(S)-2 complex (cyan) with hIL-1β as observed in the ternary complex with IL-1R1 and IL-1RAcP (salmon; PDB: 4DEP³¹). Residues previously²⁹ shown to be involved in a conformational exchange process are shown in lime green. Residues identified by CEST experiments in this study are shown in stick representation and labeled by their residue name. Note that due to high B-factors, the side-chain atoms of Lys92 and Lys94 were omitted beyond the C^β atoms by the authors of PDB: 4DEP³¹. b ¹⁵N-CEST profiles for selected residues of hIL-1β are shown. In the absence of ligand (black), the traces show two dips representing a major form of the protein in slow conformational exchange with a minor form. In the presence of the IL-1β antagonist (S)-2, peaks move to the chemical shift of the ligand-bound species (red), and the second species disappears. Note that due to only 95% saturation under our experimental conditions (K_D = 1.1 μM, P₀ = 0.8 mM, L₀ = 1.5 mM), some residual intensity at the chemical shift of the unbound species is still visible.