Expression, purification and crystallization of Aspergillus nidulans NmrA, a negative regulatory protein involved in nitrogen-metabolite repression

The NmrA repressor protein of Aspergillus nidulans was overproduced in Escherichia coli and purified to homogeneity. Gel-exclusion chromatography showed that NmrA was monomeric in solution under the buffer conditions used. The protein was crystallized in three forms, belonging to trigonal, monoclinic and hexagonal space groups. Two of these crystal forms (A and B) diffract to high resolution and thus appear suitable for structure determination. Crystal form A belongs to space group P3((1))21, with unit-cell parameters a = b = 76.8, c = 104.9 A. Crystal form B belongs to space group C2, with unit-cell parameters a = 148.8, b = 64.3, c = 110.2 A, beta = 121.8 degrees.