Biochemical Characterization of Toxoplasma gondii Mitochondrial Type II NADH Dehydrogenase Isoform I as a potential Drug Target

Abstract

Mitochondria of apicomplexan parasites such as Plasmodium falciparum and Toxoplasma gondiidisplay significant differences compared to human mitochondria, which can exploited for drug development. T. gondii lacks complex I in the respiratory chain, but expresses two "alternative" NADH dehydrogenases, which are localized to the mitochondrion as shown by epitope tagging. The absence of such "alternative" NADH dehydrogenases in the human host defines these enzymes as promising drug targets. 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 demonstrated 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 IC50 values. The efficiency of the various quinolone derivatives to inhibit TgNDH2‐I enzyme activity mirrors their potential to inhibit parasite replication in vitro, suggesting that derivatives with a long acyl site chain are promising new compounds against apicomplexan parasites.