Crystal Structures of γ-Glutamyltranspeptidase in Complex with Azaserine and Acivicin: Novel Mechanistic Implication for Inhibition by Glutamine Antagonists

Assigning Gene Function in Biosynthetic Pathways: Camalexin and Beyond

“…The observation that treatment with the Gln analog acivicin reduced camalexin production is important; however, acivicin binds to the substrate binding pocket of all GGTs (Wada et al, 2008), and it may also bind to and inhibit GGPs, which, apart from carrying out similar reactions as GGTs, are evolutionarily derived from Gln-metabolizing enzymes (Geu-Flores et al, 2009;Geu-Flores et al, 2011). An alternative explanation for the reduced camalexin production following acivicin treatment is that termination of all GGT activity could arrest glutathione and glutathione conjugates in the vacuole and extracellular space (Ferretti et al, 2009), thereby affecting glutathione availability in the cytosol.…”

“…Møldrup et al (2013) speculate that reduction of camalexin in our experiment by treatment with inhibitor acivicin (Su et al, 2011) may reflect inhibition of GGPs in addition to GGT activity. However, acivicin has been widely used as a specific inhibitor of GGT activity for in vitro and in vivo experiments of GGT (Wada et al, 2008). Crystal structure of GGT-acivicin complexes clearly revealed that acivicin binds to GGTs through several key amino acid residues in substrate binding pocket.…”

“…Crystal structure of GGT-acivicin complexes clearly revealed that acivicin binds to GGTs through several key amino acid residues in substrate binding pocket. These residues are highly conserved in GGTs from bacteria and animal cells (Wada et al, 2008). For example, Escherichia coli GGT binds acivicin through the formation of a covalent bond between the O g atom of its Thr-391 and the imino carbon of the dihydroisoxazole ring of acivicin and also through the formation of hydrogen bonds between acivicin and the GGT residues Arg-114, Asn-411, Gln-430, Asp-433, Ser-462, Ser-463, and Gly-484 (Wada et al, 2008).…”

“…These residues are highly conserved in GGTs from bacteria and animal cells (Wada et al, 2008). For example, Escherichia coli GGT binds acivicin through the formation of a covalent bond between the O g atom of its Thr-391 and the imino carbon of the dihydroisoxazole ring of acivicin and also through the formation of hydrogen bonds between acivicin and the GGT residues Arg-114, Asn-411, Gln-430, Asp-433, Ser-462, Ser-463, and Gly-484 (Wada et al, 2008). To show if Arabidopsis GGTs and GGPs also contain these conserved residues, we compared amino acid sequences of GGT1, GGT2, GGP1, and GGP3 with Ssubunits of GGTs from bacteria and animal.…”

Reply: Complexity in Camalexin Biosynthesis

“…Møldrup et al (2013) speculate that reduction of camalexin in our experiment by treatment with inhibitor acivicin (Su et al, 2011) may reflect inhibition of GGPs in addition to GGT activity. However, acivicin has been widely used as a specific inhibitor of GGT activity for in vitro and in vivo experiments of GGT (Wada et al, 2008). Crystal structure of GGT-acivicin complexes clearly revealed that acivicin binds to GGTs through several key amino acid residues in substrate binding pocket.…”