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

Glutamate decarboxylase (GAD) is a vitamin B6 enzyme which catalyzes the alpha-decarboxylation of L-glutamate to gamma-aminobutyric acid (GABA). Escherichia coli cells coexpress two highly homologous enzyme isoforms, GADalpha and GADbeta. Well diffracting crystals of GADbeta were obtained by taking advantage of the possibility of expressing each isoform separately. They belong to space group P31 or P32 with the unit-cell dimensions a = b = 115.6 and c = 206.6 A 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.