FIGURE 2.

AKR1D1·NADP⁺ complex. a, AKR1D1 adopts the (α/β)₈-barrel fold conserved among members of the AKR superfamily. Loops A, B, and C (blue) flank the steroid-binding pocket. Atoms of the catalytic tetrad and NADP⁺ are labeled and color-coded as follows: carbon, black; oxygen, red; and nitrogen, blue. The water molecule hydrogen-bonded between Tyr⁵⁸ and Glu¹²⁰ is indicated by a red sphere. Hydrogen bonds are indicated by red dashed lines. b, superposition of AKR1D1 (yellow), AKR1C9 (red), and AKR1C2 (blue) reveals significant conformational differences in loops A, B, and C.