Crystallization and preliminary X-ray crystallographic analysis of FlhD/FlhC complex from Escherichia coli

The heterotetrameric (C2D2) FlhD/FlhC complex was first discovered as a tra nscriptional activator of the flagellar genes in Escherichia coli. Recent s tudies now show that FlhD/FlhC also regulates several non-flagellar target genes in E. coli. The FlhD/FlhC complex also plays several important roles in other microorganisms. The molecular interactions between FlhD and FlhC, as well as the mechanisms by which the complex may vary its DNA-binding spe cificity, are not clear. Determination of the FlhD/FlhC crystal structure w ill provide insight into these protein-protein and protein-DNA interactions . The initial steps in this investigation are reported here: the overexpres sion, purification and crystallization of the FlhD/FlhC complex, the charac terization of this crystal form and the recording and processing of an init ial diffraction data set. The obtained crystal form of the FlhD/FlhC comple x is hexagonal (space group P6(1), unit-cell parameters a = b = 150.5, c = 115.9 Angstrom). The crystal density is very low (V-M = 5.5), with 81.7% of its volume occupied by solvent. A single C2D2 tetramer is present in the c rystallographic asymmetric unit. A complete native data set has been collec ted to 4.5 Angstrom resolution.