Monomeric isocitrate dehydrogenase in an open-conformation complex with NADP⁺

We present the crystal structure of the catalytic (ChlN/ChlB)2 complex of DPOR from the cyanobacterium Thermo¬synecho¬coccus elongatus at 2.4 Å resolution.Subunits ChlN and ChlB are structurally related to each other as well as to the subunits NifD and NifK of the MoFe-protein of nitrogenase.The intersubunit [4Fe-4S] cluster of DPOR is coordinated by 3 cysteines from ChlN, while the fourth ligand is an aspartate residue of ChlB.This coordination destabilizes the cluster dramatically making it extremely sensitive to oxygen.Although aspartatic acid residues have been known to function in iron-sulfur cluster coordination for many years, this is the first crystal structure actually demonstrating this unusual coordination.