Fig. 2: Substrate binding in the D2HDH/NAD(P)⁺/2-ketohexanoic acid complexes.

a A close up of the binding site of 2-ketohexanoic acid (yellow carbons) in the productive orientation to D2HDH (beige carbons) in the D2HDH/NADP⁺/2-ketohexanoic acid complex (NADP⁺ green carbons, pdb:9ibe) showing close proximity of the keto moiety to the nicotinamide ring and catalytic histidine. b An equivalent view of the binding of hydroxypyruvate (slate carbons) to glyoxylate reductase/hydroxypyruvate reductase (GRHPR, brown carbons, pdb:2gcg), showing the close similarity in binding and active site residues to D2HDH. c the same view of the D2HDH/NAD⁺/2-ketohexanoic acid complex (pink carbons, NAD⁺ cyan carbons, pdb:8qzb) showing the keto acid substrate (yellow carbons) in the abortive orientation, with the keto and carboxyl moieties swapped in position compared to the productive orientation. d D-2-hydroxyhexanoic acid (beige carbons) bound to the active site of the D2HDH/NADP⁺ complex (light yellow and green carbons, respectively, pdb:5mha) in the productive orientation, with the C2 hydroxyl adjacent to the catalytic histidine. The active site in this complex also contains 2-ketohexanoic acid, which has been removed from the figure for clarity (Supplementary Figs. 2c and 4). Critical hydrogen bonds are highlighted (yellow dashes) with key residues and substrate atoms labelled.