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A unique homodimeric NAD + ‐linked isocitrate dehydrogenase from the smallest autotrophic eukaryote Ostreococcus tauri
Author(s) -
Tang WangGang,
Song Ping,
Cao ZhengYu,
Wang Peng,
Zhu GuoPing
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.14-257014
Subject(s) - nad+ kinase , isocitrate dehydrogenase , biology , idh1 , biochemistry , cofactor , glycerol 3 phosphate dehydrogenase , dehydrogenase , dihydroxyacetone phosphate , enzyme , mutant , gene
In eukaryotes, NAD + ‐dependent isocitrate dehydrogenase (IDH) is strictly mitochondrial and is a key enzyme in the Krebs cycle. To date, all known NAD + ‐specific IDHs (NAD‐IDHs) in the mitochondria are believed to be heteromeric in solution. Here, a unique homodimeric NAD‐IDH from Ostreococcus tauri (OtIDH), the smallest autotrophic picoeukaryote, was unveiled. Active OtIDH has a molecular weight of ~93 kDa with each subunit of 46.7 kDa. In the presence of Mn 2+ and Mg 2+ , OtIDH displayed 42‐fold and 51‐fold preference for NAD + over NADP + , respectively. Interestingly, OtIDH exhibited a sigmoidal kinetic behavior in response to isocitrate unlike other homodimeric homologs, and a remarkably high affinity for isocitrate ( S 0.5 < 10 μM) unlike other hetero‐oligomeric homologs. Furthermore, its coenzyme specificity can be completely converted from NAD + (ancient trait) to NADP + (adaptive trait) by rational mutagenesis based on the evolutionary trace. Mutants D344R and D344R/ M345H displayed a 15‐fold and 72‐fold preference for NADP + over NAD + , respectively, indicating that D344 and M345 are the determinants of NAD + specificity. These findings also suggest that OtIDH may be an ancestral form of type II IDHs (all reported members are NADP + ‐linked enzymes) and may have evolved into NADP + ‐dependent IDH for adaptation to the increased demand of NADPH under carbon starvation.—Tang, W.G., Song, P., Cao, Z.Y., Wang, P., Zhu, G.‐P. A unique homodimeric NAD + ‐linked IDH from the smallest autotrophic eukaryote Ostreococcus tauri. FASEB J. 29, 2462‐2472 (2015). www.fasebj.org