members of the same gene family encode enzymes with either shikimate or quinate dehydrogenase activity. The poplar genome encodes five DQD/SDH-like genes (Poptr1 to Poptr5), which have diverged into two distinct groups based on sequence analysis and protein structure prediction. In vitro biochemical assays prove that Poptr1 and -5 are true DQD/SDHs, whereas Poptr2 and -3 instead have QDH activity with only residual DQD/SDH activity, cf. EC 1.1.1.282
a contact with the shikimate C1-carboxyl is formed by the phenol hydroxyl of a tyrosine. Substitution of this residue in Arabidopsis thaliana DHQ-SDH causes a substantial reduction in turnover rate
the conversion of 3-dehydroquinate to shikimate via 3-dehydroshikimate is catalyzed by the bifunctional enzyme dehydroquinate dehydratase/shikimate dehydrogenase (DQD/SDH, EC 4.2.1.10 and E.C. 1.1.1.25). The DQD domain constitutes the N-terminal half of the protein and the SDH domain the C-terminal half. Poplar DQD/SDHs have distinct expression profiles suggesting separate roles in protein and lignin biosynthesis. Shikimate is essential for protein biosynthesis
in plants, 3-dehydroshikimate from the shikimate pathway is thought to be the immediate precursor of gallate, a component of hydrolysable tannins. Metabolic pathways involving SDH family proteins: (A) the shikimate pathway, (B) the quinate pathway, (C) the aminoshikimate pathway, overview
in plants, 3-dehydroshikimate from the shikimate pathway is thought to be the immediate precursor of gallate, a component of hydrolysable tannins. Metabolic pathways involving SDH family proteins: (A) the shikimate pathway. (B) the quinate pathway. (C) the aminoshikimate pathway, overview
the shikimate pathway leads to the biosynthesis of aromatic amino acids essential for protein biosynthesis and the production of a wide array of plant secondary metabolites. 3-Dehydroquinate is the substrate for shikimate biosynthesis through the sequential actions of dehydroquinate dehydratase (DQD) and shikimate dehydrogenase (SDH) contained in a single protein in plants. Reactions comprising the shikimate/quinate cycle, overview
in plants such as Arabidopsis thaliana and Populus trichocarpa, shikimate dehydrogenase SDH is fused to an anabolic (type I) dehydroquinate dehydratase (DHQ), forming a bifunctional protein known as the DHQ-SDH complex, cf. EC 4.2.1.10 and EC 1.1.1.25. The close proximity of domains in the DHQ-SDH complex may facilitate substrate channeling between enzyme active sites, minimizing the loss of shikimate pathway intermediates to competing processe. Crystallization of the Arabidopsis thaliana protein with shikimate bound in the SDH domain and tartrate (a component of the crystallization solution) in the DHQ domain reveals a V-shaped orientation of the domains. Addition of NADP+ to DHQ–SDH crystals already containing shikimate in the SDH domain results in the production of 3-dehydroshikimate by the SDH domain and the transfer of the compound to the DHQ active sites
in plants such as Arabidopsis thaliana and Populus trichocarpa, shikimate dehydrogenase SDH is fused to an anabolic (type I) dehydroquinate dehydratase (DHQ), forming a bifunctional protein known as the DHQ–SDH complex, cf. EC 4.2.1.10 and EC 1.1.1.25. The close proximity of domains in the DHQ–SDH complex may facilitate substrate channeling between enzyme active sites, minimizing the loss of shikimate pathway intermediates to competing processes
three-dimensional protein structures homology modelling of the five putative poplar DQD/SDHs using Arabidopsis DQD/SDH enzyme structure, PDB ID c2o7qA, of the enzyme coupled with either 3-dehydroshikimate and tartrate or shikimate, as a template
the bifunctional enzyme dehydroquinate dehydratase/shikimate dehydrogenase (DQD3/SDH cf. EC 4.2.1.10 and EC 1.1.1.25) catalyzes the the conversion of 3-dehydroquinate to shikimate via 3-dehydroshikimate
The bifunctional enzyme also catalyzes dehydration of 3-dehydroquinate to 3-dehydroshikimate. Under saturating conditions, Poptr5 displays strong activity with shikimate but no detectable activity with quinate even at elevated enzyme concentrations. The isozyme shows no quinate hydrolyase activity
the bifunctional enzyme dehydroquinate dehydratase/shikimate dehydrogenase (DQD3/SDH cf. EC 4.2.1.10 and EC 1.1.1.25) catalyzes the the conversion of 3-dehydroquinate to shikimate via 3-dehydroshikimate
the DQD domain constitutes the N-terminal half of the protein and the SDH domain the C-terminal half. Three-dimensional protein structures homology modelling of the five putative poplar DQD/SDHs using Arabidopsis DQD/SDH enzyme structure, PDB ID c2o7qA, of the enzyme coupled with either 3-dehydroshikimate and tartrate or shikimate, as a template
the DQD domain constitutes the N-terminal half of the protein and the SDH domain the C-terminal half. Three-dimensional protein structures homology modelling of the five putative poplar DQD/SDHs using Arabidopsis DQD/SDH enzyme structure, PDB ID c2o7qA, of the enzyme coupled with either 3-dehydroshikimate and tartrate or shikimate, as a template