Heterologous expression and purification of glutamate decarboxylase-1 from the model plant Arabidopsis thaliana: Characterization of the enzyme's in vitro truncation by thiol endopeptidase activity.

Plant glutamate decarboxylase (GAD) is a Ca-calmodulin (CaM) activated enzyme that produces γ-aminobutyrate (GABA) as the first committed step of the GABA shunt. Our prior research established that in vivo phosphorylation of AtGAD1 (AT5G17330) occurs at multiple N-terminal serine residues following Pi resupply to Pi-starved cell cultures of the model plant Arabidopsis thaliana. The aim of the current investigation was to purify recombinant AtGAD1 (rAtGAD1) following its expression in Escherichia coli to facilitate studies of the impact of phosphorylation on its kinetic properties.