Purification, crystallization and preliminary X-ray analysis of a complex between granulocyte colony-stimulating factor and its soluble receptor

Crystals of the complex between granulocyte colony-stimulating factor and its soluble receptor were obtained by a vapour-diffusion method using ammonium sulfate as a precipitant. Addition of 1,4-dioxane was critical in order to grow the crystals to sufficient sizes. Cryoprotection was essential in order to collect diffraction data at atomic resolution. Two kinds of crystal forms were obtained depending on the cryoprotectants. In a cryosolvent with the same salt concentration as in the crystallization conditions, the crystal belonged to the space group I4(1)22. At higher salt concentrations, the crystal was converted to a different space group P4(1)2(1)2 (P4(3)2(1)2) with the same unit-cell parameters.