Crystallization of a recombinant form of the complete sequence of human γ-interferon: characterization by small-angle X-ray scattering, mass spectrometry and preliminary X-ray diffraction studies

The crystallization conditions of a recombinant form of the complete sequence of human γ‐interferon, designated r‐hu IFN‐γ (RU 42369), have been determined after studying the behaviour of this protein in solution by small‐angle X‐ray scattering (SAXS) as a function of pH and salt type. IFN‐γ is difficult to crystallize without truncating at least the last five amino acids of the C‐terminus; the SAXS results suggest viable crystallization conditions that led to crystals of r‐hu IFN‐γ suitable for X‐ray diffraction analysis. The crystals were grown in the presence of ammonium sulfate using vapour‐diffusion techniques. The crystals, which diffract to 5 Å resolution at best, belong to the primitive tetragonal space group P4212 and have unit‐cell parameters a = b = 123.4, c = 93.4 Å. The protein contained in these crystals was analyzed by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS), which verified the presence of the complete amino‐acid sequence of r‐­hu IFN‐γ.