Purification, crystallization and preliminary crystallographic studies of the complex of interferon-λ1 with its receptor

Human interferon-λ1 (IFN-λ1_Ins) and the extracellular domain of interferon-λ1 receptor (IFN-λ1R1) were expressed in Drosophila S2 cells and purified to homogeneity. Both IFN-λ1_Ins and interferon-λ1 produced from Escherichia coli (IFN-λ1_Bac) were coupled with IFN-λ1R1 at room temperature and the complexes were purified by gel filtration. Both complexes were crystallized; the crystals were flash-frozen at 100 K and diffraction data were collected to 2.16 and 2.1 Å, respectively. Although the IFN-λ1_Bac–IFN-λ1R1 and IFN-λ1_Ins–IFN-­λ1R1 complexes differed only in the nature of the expression system used for the ligand, their crystallization conditions and crystal forms were quite different. A search for heavy-atom derivatives as well as molecular-replacement trials are in progress.