Characterization of two crystal forms of Clostridium thermocellum endoglucanase CelC

Endoglucanase CelC from Clostridium thermocellum expressed in Escherichia coli has been crystallized in two different crystal forms by the hanging drop method. Crystals of form I were grown with polyethylene glycol as a precipitant. They are orthorhombic, space group P2(1)2(1)2(1), with cell dimensions a = 51.4 A, b = 84.3 A, and c = 87.5 A. Crystals of form II, obtained in ammonium sulfate solutions, belong to the tetragonal space group P4(1)2(1)2 (or P4(3)2(1)2) with cell dimensions of a = b = 130.7 A and c = 69.6 A. Diffraction data to 2.8 A resolution were observed for both crystal forms with a rotating anode generator. Preliminary oscillation images of the orthorhombic form I crystals using a synchrotron radiation source show diffraction to 2.2 A resolution, indicating that these crystals are suitable for high resolution crystallographic analysis.