A comparison of the Y7F/D72N-LlNDT-2 and WT-LlNDT-2 (9F09) complexes with cytidine and 2'-deoxycytidine respectively (Figure ) shows close agreement between the atom positions of the active site sidechains and ligands in each structure. These include those between the 5'-OH and D92, and the OE2 E98 carboxylate oxygen and the 3'-OH of (deoxy)ribose. However, the side chain of N72, which, like that of D72 in the WT-LlNDT-2, forms an interaction with the O2 of cytosine, has different rotamer conformations in each monomer in the asymmetric unit, one of which permits two interactions with cytidine (Figure ). In addition, in the Y7F/D72N structure, the interactions between the nucleobase of 8 and the side chain of Q46 are slightly different, with the interaction between the nitrogen of the amide and the O2 of 8 observed in the WT complex disrupted by a movement of the Q46 side chain. Selected active site-ligand interactions are illustrated with black dashed lines with distances in Å.