Crystallization of a recombinant form of the complete sequence of human gamma-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 sequen ce of human gamma -interferon, designated r-hu IFN-gamma (RU 42369), have b een 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- gamma is difficult to crystallize without truncating at least the last five amino acids of the C-terminus; the SAXS results suggest viable crystalliza tion conditions that led to crystals of r-hu IFN-gamma suitable for X-ray d iffraction analysis. The crystals were grown in the presence of ammonium su lfate using vapour-diffusion techniques. The crystals, which diffract to 5 Angstrom resolution at best, belong to the primitive tetragonal space group P42(1)2 and have unit-cell parameters a = b = 123.4, c = 93.4 Angstrom. Th e protein contained in these crystals was analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), which verified the pre sence of the complete amino-acid sequence of r-hu IFN-gamma.