Preparation, crystallization and preliminary X-ray diffraction studies of the glycosylated form of human interleukin-23

Interleukin-23 (IL-23), a member of the IL-12 family, is a heterodimeric cytokine composed of p19 and p40 subunits. IL-23 plays crucial roles in the activation, proliferation and survival of IL-17-producing helper T cells which induce various autoimmune diseases. Human p19 and p40 subunits were cloned and coexpressed in N-acetylglucosaminyltransferase I-negative 293S cells, which produce high-mannose-type glycosylated proteins in order to diminish the heterogeneity of modified N-linked glycans. The glycosylated human IL-23 was purified and crystallized by the hanging-drop vapour-diffusion method. X-ray diffraction data were then collected to 2.6 Å resolution. The crystal belonged to space group P6₁ or P6₅, with unit-cell parameters a = b = 108.94, c = 83.79 Å, γ = 120°. Assuming that the crystal contains one molecule per asymmetric unit, the calculated Matthews coefficient was 2.69 ų Da⁻¹, with a solvent content of 54.2%. The structure was determined by the molecular-replacement method, with an initial R factor of 52.6%. After subsequent rigid-body and positional refinement, the R_work and R_free values decreased to 31.4% and 38.7%, respectively.