EC Number   |
General Information |
Reference |
|---|
   1.1.1.24 | evolution |
plant SDH enzymes are fused to dehydroquinate dehydratases (DQDs, EC 4.2.1.10) to form bifunctional DQD/SDH enzymes. The DQD activity is observed for EcDQD/SDH1, 2, and 3, but not for EcDQD/SDH4a. Among the active enzymes, EcDQD/SDH1 exhibits the highest DQD activity, followed by EcDQD/SDH2 (about 50% of the EcDQD/SDH1 activity) and EcDQD/SDH3 (about 5% of the EcDQD/SDH1 activity). For shikimate formation from 3-DHS as well as shikimate oxidation to 3-DHS, measurable catalytic activities are detected for EcDQD/SDH1-3, but the activities of EcDQD/SDH2 and 3 are less than 20% of those of EcDQD/SDH1. Regarding the cofactor, EcDQD/SDH1-3 have a clear preference for NADPH/NADP+ over NADH/ NAD+. In contrast, EcDQD/SDH4a and b lack shikimate formation activity. For the reverse reaction, the conversion of shikimate to 3-DHS, EcDQD/SDH4a and b display low enzymatic activity with a preference for NAD+ as the cofactor. Both EcDQD/SDH2 and 3 exhibit relatively high gallate formation activity, in contrast to the low activity of EcDQD/SDH1. The preferred cofactor in this reaction is NADP+. The reversible quinate formation from 3-DHQ is catalyzed only by EcDQD/SDH4a/b, with NADH/NAD+ as the preferred cofactor. The reaction specificity of EcDQD/SDH4a confirms the sequence-based prediction that EcDQD/SDH4a is a functional QDH enzyme. This enzyme should be renamed EcQDHa and its closest relative, EcDQD/SDH4b, should be renamed EcQDHb. The EcDQD/SDH4a and EcDQD/SDH4b genes may represent allelic variants encoding enzymes with 99.2% amino acid identity |
762187 |
| 1.1.1.24 | evolution |
the enzyme belongs to the QDH family, phylogenetic reconstruction of the SDH/QDH gene family across land plants, overview. SDH and QDH belong to the same gene family, which diverged into two phylogenetic clades after a defining gene duplication just prior to the angiosperm/gymnosperm split. Non-seed plants that diverged before this duplication harbour only a single gene of this family. Extant representatives from the chlorophytes (Chlamydomonas reinhardtii), bryophytes (Physcomitrella patens) and lycophytes (Selaginella moellendorfii) encoded almost exclusively SDH activity in vitro. A reconstructed ancestral sequence representing the node just prior to the gene duplication also encoded SDH activity. Quinate dehydrogenase activity was gained only in seed plants following gene duplication. Quinate dehydrogenases of gymnosperms, e.g. Pinus taeda, may be reminiscent of an evolutionary intermediate since they encode equal SDH and QDH activities. The second copy in Pinus taeda maintains specificity for shikimate similar to the activity found in the angiosperm SDH sister clade. The codon for a tyrosine residue within the active site displays a signature of positive selection at the node defining the QDH clade, where it changed to a glycine. Replacing the tyrosine with a glycine in a highly shikimate-specific angiosperm SDH is sufficient to gain some QDH function. Thus, very few mutations are necessary to facilitate the evolution of QDH genes. The two proteins from Pinus taeda are chosen to represent the post-duplication SDH and QDH clades from gymnosperms. The single-copy genes from Selaginella moellendorffii, Physcomitrella patens and Chlamydomonas reinhardtii are selected to represent the pre-duplication lycopod, bryophyte and green algal clades, respectively. Thr381 is conserved in most members across all SDH clades but was replaced under positive selection by Gly in the branch leading into the seed plant QDH clade |
762146 |
| 1.1.1.24 | metabolism |
link between reactions catalysed by the shikimate pathway enzyme dehydroquinate dehydratase (DQD)/shikimate dehydrogenase (SDH) and quinate dehydrogenase (QDH) involved in quinate metabolism. Shikimate is produced from dehydroquinate via a two-step reaction and subsequently channelled to downstream reactions in the pathway. Quinate is reversibly formed from a side branch of the shikimate pathway from dehydroquinate and may be converted to more structurally complex secondary metabolites or to dehydroquinate to fuel the shikimate pathway |
762146 |
