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

Glutamate decarboxylase (GAD) is a vitamin B₆ enzyme which catalyzes the α-decarboxylation of L-glutamate to γ-aminobutyric acid (GABA). Escherichia coli cells coexpress two highly homologous enzyme isoforms, GADα and GADβ. Well diffracting crystals of GADβ 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 Å 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.