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Crystallization of purified recombinant human interleukin‐1β

The gene for human interleukin‐1β was cloned from SK‐hep‐1 hepatoma cellular RNA and expressed at high levels in Escherichia coli both as the naturally processed form (rIL‐1β) and as a variant with an additional sequence of three amino acids on the N‐terminus (rIL‐1β+). Expressed protein was purified to homogeneity by a sequence of steps, which included low pH incubation, adsorption and desorption from Procion Red Sepharose, sizing on a Superose 12 fast‐performance liquid chromatography (FPLC) column, and anion exchange chromatography on QAE Sepharose. The final step provided a biologically active protein that migrates on twodimensional (2‐D) gels as a single spot with a pI of 6.7 ± 0.2 and a molecular mass of 17,500 daltons. Concentrated solutions of rIL‐1β have produced crystals by ammonium sulfate precipitation. The crystals are tetragonal, show the symmetry of space group P41 or its enantiomer, have lattice constants of a = 58.46 (1) and c = 77.02 (3) A, and scatter to at least 2 Å resolution. A structure determination based on these crystals is under way.