Crystallization and preliminary X-ray crystallographic analysis of carboxyl-terminal region 4 of SigR from Streptomyces coelicolor A3(2)

Full-length SigR from Streptomyces coelicolor A3(2) was overexpressed in Escherichia coli, purified and submitted to crystallization trials using either polyethylene glycol 3350 or 4000 as a precipitant. X-ray diffraction data were collected to 2.60 angstrom resolution under cryoconditions using synchrotron X-rays. The crystal packs in space group P4(3)2(1)2, with unit-cell parameters a = b = 42.14, c = 102.02 angstrom. According to the Matthews coefficient, the crystal asymmetric unit cannot contain the full-length protein. Molecular replacement with the known structures of region 2 and region 4 as independent search models indicates that the crystal contains only the -35 element-binding carboxyl-terminal region 4 of full-length SigR. Mass-spectrometric analysis of the harvested crystal confirms this, suggesting a crystal volume per protein weight (V-M) of 2.24 angstrom(3) Da(-1) and 45.1% solvent content.