To explore the structural implications of the differences between the two enzymes, WT-LlNDT-2 and the Y7F/D72N mutant were both crystallised using conditions determined for the WT-LlNDT-2 enzyme previously. Complexes were obtained by soaking cytidine 8 into the crystals. All structures contained two molecules in the asymmetric unit, constituting one third of the hexamer routinely observed in solution. In the case of WT-LlNDT-2, electron density in the omit maps obtained could be clearly modelled as the ribosylated intermediate (Figure ), and the cleaved cytosine nucleobase, whereas in the Y7F/D72N structure cytidine (8) was intact (Figure ), presumably reflective of its poorer kcat as observed for CtNDT. A comparison of the ribosylated WT-LlNDT-2 structure with that of the 2'-deoxyribosylated structure previously obtained by our groups (9F08), shows only a small rotation of the ribose ring towards the side chain of D92, resulting in a slightly extended interaction of 2.9 Å between the 3'-OH and the OE2 atom of E98 compared to the 2'-deoxyribosylated complex (2.7 Å). By contrast, the ribosylated intermediate of CtNDT reported by Tang and co-workers features the ribose flipped approximately 90° from this position, with the 2'-OH interacting with the side chain of D62 (D72 in LlNDT-2), despite the conservation of most active site residues, although the authors report multiple conformations of the ligand in this complex, evidenced by ambiguous electron density.