Expression, purification and preliminary X-ray analysis of crystals of Bacillus subtilis glutamate racemase

Glutamate racemase (MurI, RacE; E.C.5.1.1.3) catalyses the cofactor-independent conversion of L-glutamate to D-glutamate, an essential step in the synthesis of components of the bacterial cell wall. The gene for RacE from Bacillus subtilis has been cloned and the protein expressed in Escherichia coli, purified and crystallized in the presence of L-glutamate using the hanging-drop method of vapour diffusion with diammonium tartrate as the precipitant. The crystals belong to the monoclinic space group C2, with approximate unit-cell parameters a = 133.6, b = 60.1, c = 126.2 A, beta = 117.6 degrees . Consideration of the possible values of V(M) suggests that the asymmetric unit contains either two (V(M) = 3.75 A(3) Da(-1)) or three (V(M) = 2.5 A(3) Da(-1)) subunits. The crystals diffract X-rays to at least 2.1 A resolution on a synchrotron-radiation source and are suitable for structural studies. Determination of the structure may provide insight into the molecular basis of substrate recognition and catalysis by this enzyme.