Distribution and functional analysis of isocitrate dehydrogenases across kinetoplastids.

Isocitrate dehydrogenase (IDH) is an enzyme converting isocitrate to α-ketoglutarate in the canonical tricarboxylic acid (TCA) cycle. There are three different types of IDH documented in eukaryotes. Our study points out the complex evolutionary history of IDHs across kinetoplastids, where the common ancestor of Trypanosomatidae and Bodonidae was equipped with two isoforms of the IDH enzyme: the NADP+-dependent IDH1 with possibly dual localization in the cytosol and mitochondrion and NADP+-dependent mitochondrial IDH2. In the extant trypanosomatids, IDH1 is present only in a few species suggesting that it was lost upon separation of Trypanosoma spp. and replaced by the mainly NADP+-dependent cytosolic IDH3 of bacterial origin in all the derived lineages. In this study, we experimentally demonstrate that the omnipresent IDH2 has a dual localization in both mitochondrion and cytosol in at least four species that possess only this isoform. The apparent lack of the NAD+-dependent IDH activity in trypanosomatid mitochondrion provides further support to the existence of the non-canonical TCA cycle across trypanosomatids and the bidirectional activity of IDH3 when operating with NADP+ cofactor instead of NAD+. This observation can be extended to all 17 species analyzed in this study, except for Leishmania mexicana which showed only low IDH activity in the cytosol. The variability in isocitrate oxidation capacity among species may reflect the distinct metabolic strategies and needs for reduced cofactors in particular environments.