title: The Toxoplasma gondii type-II NADH dehydrogenase TgNDH2-I is inhibited by 1-hydroxy-2-alkyl-4(1H)quinolones.
abstract: The apicomplexan parasite Toxoplasma gondii does not possess complex I of the mitochondrial respiratory chain, but has two genes encoding rotenone-insensitive, non-proton pumping type-II NADH dehydrogenases (NDH2s). The absence of such "alternative" NADH dehydrogenases in the human host defines these enzymes as potential drug targets. TgNDH2-I and TgNDH2-II are constitutively expressed in tachyzoites and bradyzoites and are localized to the mitochondrion as shown by epitope tagging. Functional expression of TgNDH2-I in the yeast Yarrowia lipolytica as an internal enzyme, with the active site facing the mitochondrial matrix, permitted growth in the presence of the complex I inhibitor DQA. Bisubstrate kinetics of TgNDH2-I measured within Y. lipolytica mitochondrial membrane preparations were in accordance with a ping-pong mechanism. Using inhibition kinetics we demonstrate here that 1-hydroxy-2-alkyl-4(1)quinolones with long alkyl chains of C(12) (HDQ) and C(14) are high affinity inhibitors for TgNDH2-I, while compounds with shorter side chains (C(5) and C(6)) displayed significantly higher IC(50) values. The efficiency of the various quinolone derivatives to inhibit TgNDH2-I enzyme activity mirrors their inhibitory potency in vivo, suggesting that a long acyl site chain is critical for the inhibitory potential of these compounds.
authors.affiliation: Institute of Medical Microbiology, University of Göttingen, Kreuzbergring 57, Göttingen D-37075, Germany.
authors.forename: San San
authors.initials: SS
authors.lastname: Lin
authors.forename: Stefan
authors.initials: S
authors.lastname: Kerscher
authors.forename: Ahmad
authors.initials: A
authors.lastname: Saleh
authors.forename: Ulrich
authors.initials: U
authors.lastname: Brandt
authors.forename: Uwe
authors.initials: U
authors.lastname: Gross
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bohne
mesh_terms: D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008856:Microscopy, Fluorescence; D009245:NADH Dehydrogenase / Q000037:antagonists & inhibitors* / Q000235:genetics; D016366:Open Reading Frames; D015363:Quinolones / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014122:Toxoplasma / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D015363:Quinolones; D009245:NADH Dehydrogenase