Crystallization and preliminary X-ray analysis of the β-isoform of glutamate decarboxylase from Escherichia coli

Glutamate decarboxylase (GAD) is a vitamin B-6 enzyme which catalyzes the alpha-decarboxylation of L-glutamate to gamma-aminobutyric acid (GABA). Escherichia coli cells coexpress two highly homologous enzyme isoforms, GAD alpha and GAD beta. Well diffracting crystals of GAD beta were obtained by taking advantage of the possibility of expressing each isoform separately. They belong to space group P3(1) or P3(2) with the unit-cell dimensions a = b = 115.6 and c = 206.6 Angstrom and contain one GAD hexamer in the asymmetric unit. High-resolution synchrotron data were collected at 100 K for the native protein and a potential heavy-atom derivative.