Fig. 3: Cofactor adenine ribose interactions.

a A close up of the binding site of the adenine ribose ring in the NADP⁺/D2HDH/2-ketohexanoic acid complex (beige carbons, pdb:9ibe) showing the position of the cofactor (green) the 2’ phosphate, and interactions to the protein (yellow dashes). b The same view for the NAD⁺/D2HDH/2-ketohexanoic acid complex (pink carbons, cyan NADP⁺, pdb:8qzb), showing the chloride ion (green sphere) binding in the equivalent position to the 2’ phosphate of NADP⁺. c Equivalent view of the NAD⁺/D2HDH/2-ketohexanoic acid/sulfate complex (white carbons, pdb:5mh6) showing the associated sulfate ion (yellow) binding in a similar position to the Cl^- ion. d A cartoon representation of the superimposed co-factor binding domains of the NAD⁺/SO₄ and NADP⁺/2-keto acid complexes (coloured as above) highlighting differences in position of the sulfate compared to the ribose phosphate and illustrating the movement of the wing of this domain (Gly 163 - Ala 190) to accommodate the sulfate in the NAD⁺/SO₄ complex. In all the complexes the positioning the co-factor nicotinamide ring and 2-keto acid substrate (2-KHA, yellow) is essentially identical.