FIGURE 3.

a, schematic and molecular surface representations of apo-LigL and the LigL·NADH·(αS,βR)-GGE complex. The substrate binding loop (residues 191–229) is completely disordered in the apo-LigL structure. In the LigL·NADH·(αS,βR)-GGE complex structure the substrate binding loop region (magenta) acts as a lid above the NADH and GGE binding sites. b, the active site of LigL in complex with NADH showing the interactions involving the co-substrate NADH. Residue Asp³⁶ contacts the 2′- and 3′-hydroxyl groups of the adenosine ribose sugar, the catalytic residues Tyr¹⁵⁸ and Lys¹⁶² contact the nicotinamide ribose sugar, the nicotinamide moiety interacts with the main chain nitrogen atom from Ile¹⁹¹, and the phosphate groups interact with side chain atoms from Ser¹⁹³ and the main chain nitrogen atom from Arg¹⁹⁴. c, the substrate binding site for LigL·NADH·(αS,βR)-GGE showing residues Asp⁹⁵, Ser¹⁴⁴, Tyr¹⁵⁸, Pro¹⁸⁸, and Arg²²² that interact directly with the GGE substrate. d, active site of LigL·NADH·(αS,βR)-GGE showing the catalytic tetrad N¹¹⁵-S¹⁴⁴-Y¹⁵⁸-K¹⁶² and a water molecule (W75) involved in the extended proton relay system described for the SDR family (24). Broken lines represent hydrogen bonds, and distances are shown in Å.