Crystallization and preliminary X-ray crystallographic analysis of the cysteine protease inhibitor clitocypin

Clitocypin is a cysteine protease inhibitor from the mushroom Clitocybe nebularis. The protein has been purified from natural sources and crystallized in a variety of non-isomorphous forms belonging to monoclinic and triclinic space groups. A diffraction data set to 1.55 A resolution was obtained from a crystal belonging to space group P2, with unit-cell parameters a = 38.326, b = 33.597, c = 55.568 A, beta = 104 degrees. An inability to achieve isomorphism forced the use of MAD and SAD phasing methods. Phasing is in progress.