INITIAL CRYSTALLOGRAPHIC ANALYSIS OF A RECOMBINANT HUMAN INTERLEUKIN-1 RECEPTOR ANTAGONIST PROTEIN

We report the crystallization of samples of a recombinant preparation of human interleukin-I receptor antagonist protein (IRAP) and solution of the crystal structure by isomorphous replacement methods. Crystals were obtained by the hanging-drop vapor-diffusion method at 277 K fro m solutions of PEG 4000 containing sodium chloride, dithiothreitol and PIPES [sodium piperazione-N,N'-bis(2-ethanesulfonate)] buffer at pH 7 .0. Crystals appear within about a week and grow as truncated tetragon al bipyramids to 0.3-0.6 mm on an edge. X-ray diffraction data from th ese crystals specify space group P4(3)2(1)2 and unit-cell dimensions o f a = b = 72.35 (26), c = 114.7 (8) angstrom and Z = 16 (two molecules per asymmetric unit). Fresh crystals diffract to about 2.3 angstrom r esolution. The search for heavy-atom derivatives has produced two, pot assium gold cyanide and trimethyl lead chloride, as same-site, single- site derivatives. Inspection of an electron-density map at 4 angstrom resolution calculated with these derivatives confirms that the IRAP mo lecule is a member of the interleukin-I structural family.