A common structural basis for pH- and calmodulin-mediated regulation in plant glutamate decarboxylase

Glutamate decarboxylase (Gad) catalyzes glutamate to γ-aminobutyrateconversion. Plant Gad is a ∼340 kDa hexamer, involved in development andstress response, and regulated by pH and binding of Ca2+/calmodulin(CaM) to the C-terminal domain. We determined the crystal structure ofArabidopsis thaliana Gad1 in its CaM-free state, obtained a low-resolutionstructure of the calmodulin-activated Gad complex by small-angle X-rayscattering and identified the crucial residues, in the C-terminal domain, forregulation by pH and CaM bindin