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
Résumé
The crystallization conditions of a recombinant form of the complete sequence of human $\gamma$-interferon, designated r-hu IFN-$\gamma$ (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-$\gamma$ 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-$\gamma$ 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 P42$_1$2 and have unit-cell parameters a = b = 123.4, c = 93.4 Å. The protein contained in these crystals was analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), which verified the presence of the complete amino-acid sequence of r-hu IFN-$\gamma$.