Structure of PnpE-NAD complex. A. The difference electron density map (2Fo-Fc) calculated at 3.1 Å resolution using phase from the final model with NAD and contoured at 1.0σ reveals the existence of NAD with faily electron density within molecule A. B. PnpE cofactor and substrate binding domains. The yellow cartoon stands for the substrate binding domain and the green cartoon represents the cofactor binding domain. NAD is shown in sticks. C. Structure comparison of the apo and NAD bound PnpE. Yellow ribbon represents the apo-PnpE structure; Green ribbon stands for the NAD bound structure. The NAD is shown in color sticks. Six amino acids (C281, E247, Q210, W148, I146 and K172) interact with the cofactor. These amino acids are shown in stick. The dash region has the most significant structure discrimination and E247 moves the most.