Crystallization and preliminary X-ray analyses of catabolite control protein A, free and in complex with its DNA-binding site

The catabolite control protein (CcpA) from Bacillus megaterium is a member of the bacterial repressor protein family GalR/LacI. CcpA with an N-termina l His-tag was used for crystallization. Crystals of free CcpA and of CcpA i n complex with the putative operator sequence (catabolite responsive elemen ts, CRE) were obtained by vapour-diffusion techniques at 291 K using the ha nging-drop method. CcpA crystals grown in the presence of polyethylene glyc ol 8000 belong to the hexagonal space group P6(1)22 or P6(5)22, with unit-c ell parameters a = 74.4, c = 238.8 Angstrom. These crystals diffract X-rays to 2.55 Angstrom resolution and contain one monomer of the homodimeric pro tein per asymmetric unit. Crystals of the CcpA-CRE complex were obtained wi th ammonium sulfate as precipitant and belong to the tetragonal space group I4(1)22, with unit-cell parameters a = 125, c = 400 Angstrom and one compl ex per asymmetric unit. Although these cocrystals grew to a sufficient size , X-ray diffraction was limited to 8 Angstrom resolution.