Abstract
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. Among them, quinate is an astringent feeding deterrent that can be formed in a single step reaction from 3-dehydroquinate catalyzed by quinate dehydrogenase (QDH). 3-Dehydroquinate is also the substrate for shikimate biosynthesis through the sequential actions of dehydroquinate dehydratase (DQD) and shikimate dehydrogenase (SDH) contained in a single protein in plants. The reaction mechanism of QDH resembles that of SDH. 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 proved that Poptr1 and -5 are true DQD/SDHs, whereas Poptr2 and -3 instead have QDH activity with only residual DQD/SDH activity. Poplar DQD/SDHs have distinct expression profiles suggesting separate roles in protein and lignin biosynthesis. Also, the QDH genes are differentially expressed. In summary, quinate (secondary metabolism) and shikimate (primary metabolism) metabolic activities are encoded by distinct members of the same gene family, each having different physiological functions.
Highlights
Quinate is an astringent feeding deterrent that can be formed in a single step reaction from 3-dehydroquinate catalyzed by quinate dehydrogenase (QDH). 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
Sequence Diversity in the DQD/SDH Superfamily—The poplar genome contains five genes annotated as DQD/SDHs (Poptr1 to Poptr5) [18]
Sequence similarity comparison of these proteins with characterized plant enzymes from Arabidopsis, tobacco, and tomato revealed that Poptr1 and Poptr5 share higher sequence similarity with characterized DQD/ SDHs than Poptr2, Poptr3, and Poptr4 (Table 2)
Summary
We demonstrate that the five putative poplar DQD/SDHs represent two functionally distinct groups, one of which preferentially uses quinate (QDH) as a substrate in vitro with only residual SDH activity, while the other has only DQD/SDH activity Expression variation among these homologues suggests distinct functions of isoforms in both plant development and adaptive responses to stresses. Chlorogenic acid is gaining interest in pharmaceutical research due to its potential role as a weight loss supplement and its association with a lower risk of type II diabetes [24] and cardiovascular diseases [25] Both quinate and shikimate can be used as chiral starting materials in the synthesis of antiviral drugs, including oseltamivir (Tamiflu, Ref. 26).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
