Expression, purification, crystallization and preliminary X-ray analysis of the native class C beta-lactamase from Enterobacter cloacae 908R and two mutants

Crystals have been obtained of the Enterobacter cloacae 908R beta -lactamas e and two point mutants by the vapour-diffusion method using similar condit ions [pH 9.0, polyethylene glycol (M-r = 6000) as precipitant]. The three c rystal forms belong to the orthorhombic space group P2(1)2(1)2, with roughl y the same unit-cell parameters; i.e. for the wild-type crystals a = 46.46, b = 82.96, c = 95.31 Angstrom. In the best cases, the crystals diffract to about 2.1 Angstrom resolution on a rotating-anode X-ray source at room tem perature. Co-crystallization experiments of poor substrates with the wild-t ype protein and the active-site serine mutant (S64C) are planned and should lead to a better understanding of the catalytic mechanism of class C beta -lactamases.