Crystallization studies of glycosylated and unglycosylated human recombinant interleukin‐2

Glycosylated interleukin‐2 (glyIL‐2) has been crystallized in two crystal forms, and unglycosylated interleukin‐2 (uIL‐2) has been crystallized in three forms. The glycosylated form of the human recombinant IL‐2 has been crystallized from 1.9 M ammonium sulfate, pH 6.5 to 7.0 in the hexagonal space group P6₂22 or its enantiomorph. The crystals diffract to 2.8 Å and contain two or three molecules per asymmetric unit. A second crystal form grows from 1.4 to 1.5 M ammonium sulfate in 0.2 M ammonium acetate, pH 5.0–5.5, as polycrystalline rosettes which are not suitable for even a preliminary crystallographic analysis. The uIL‐2 crystallizes from 1.0 to 1.7 M ammonium sulfate, 0.2 M ammonium acetate, pH 4.5–5.6 in the monoclinic space group P2₁, and less frequently in the orthorhombic space group P2₁2₁2₁ from 2.5 M ammonium sulfate, pH 4.5 to 5.7. Cross‐seeding uIL‐2 with seeds from hexagonal crystals of glyIL‐2 promotes nucleation of trigonal crystals of unglycosylated IL‐2. These trigonal crystals belong to the space group P3₁21 or its enantiomorph, with similar cell dimensions to the glyIL‐2 hexagonal crystals.