p-Hydroxyphenylpyruvate dioxygenase is a herbicidal target site for beta-triketones from Leptospermum scoparium.
p-Hydroxyphenylpyruvate dioxygenase (HPPD) is a key enzyme in tyrosine catabolism and is the molecular target site of beta-triketone pharmacophores used to treat hypertyrosinemia in humans. In plants, HPPD is involved in the biosynthesis of prenyl quinones and tocopherols, and is the target site of beta-triketone herbicides. The beta-triketone-rich essential oil of manuka (Leptospermum scoparium), and its components leptospermone, grandiflorone and flavesone were tested for their activity in whole-plant bioassays and for their potency against HPPD. The achlorophyllous phenotype of developing plants exposed to manuka oil or its purified beta-triketone components was similar to that of plants exposed to the synthetic HPPD inhibitor sulcotrione. The triketone-rich fraction and leptospermone were approximatively 10 times more active than that of the crude manuka oil, with I50 values of 1.45, 0.96 and 11.5 microg mL(-1), respectively. The effect of these samples on carotenoid levels was similar. Unlike their synthetic counterpart, steady-state O2 consumption experiments revealed that the natural triketones were competitive reversible inhibitors of HPPD. Dose-response curves against the enzyme activity of HPPD provided apparent I50 values 15.0, 4.02, 3.14, 0.22 microg mL(-1) for manuka oil, triketone-rich fraction, leptospermone and grandiflorone, respectively. Flavesone was not active. Structure-activity relationships indicate that the size and lipophilicity of the side-chain affected the potency of the compounds. Computational analysis of the catalytic domain of HPPD indicates that a lipophilic domain proximate from the Fe2+ favors the binding of ligands with lipophilic moieties.
Dayan
Franck E
FE
United States Department of Agriculture, Agricultural Research Service, Natural Products Utilization Research Unit, P.O. Box 8048, University, MS 38677, USA. fdayan@olemiss.edu
Duke
Stephen O
SO
Sauldubois
Audrey
A
Singh
Nidhi
N
McCurdy
Christopher
C
Cantrell
Charles
C
D015111:4-Hydroxyphenylpyruvate Dioxygenase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000302:isolation & purification / Q000633:toxicity; D008401:Gas Chromatography-Mass Spectrometry; D006540:Herbicides / Q000737:chemistry* / Q000302:isolation & purification / Q000633:toxicity*; D007659:Ketones / Q000737:chemistry* / Q000302:isolation & purification / Q000633:toxicity*; D031649:Leptospermum / Q000737:chemistry / Q000378:metabolism*; D018545:Lactuca / Q000187:drug effects; D008958:Models, Molecular; D015394:Molecular Structure
D004791:Enzyme Inhibitors; D006540:Herbicides; D007659:Ketones; D015111:4-Hydroxyphenylpyruvate Dioxygenase