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

Crystals have been obtained of the Enterobacter cloacae 908R β-lactamase and two point mutants by the vapour-diffusion method using similar conditions [pH 9.0, polythylene glycol (M_r= 6000) as precipitant]. The three crystal forms belong to the orthorhombic space group P2₁2₁2, with roughly the same unit-cell parameters; i.e. for the wild-type crystals a = 46.46, b = 82.96, c = 95.31 Å. In the best cases, the crystals diffract to about 2.1 Å resolution on a rotating-anode X-ray source at room temperature. Co-crystallization experiments of poor substrates with the wild-type protein and the active-site serine mutant (S64C) are planned and should lead to a better understanding of the catalytic mechanism of class C β-lactamases.