Fig. 4: Substrate binding modes in ClCdnE and LpCdnE.

The bound nucleotides are shown as thick stick models and the amino acid residues as thin sticks. The magnesium ion and the associated water molecules are shown as spheres. Hydrogen bonds and coordinate bonds are indicated by using dashed lines. The models are superimposed on the Fo-Fc maps each calculated by omitting the atoms in question and contoured at 4-σ level. In (A), the view is centered on the donor nucleotide in the ClCdnE-UTP complex; in (B) it is centered on the acceptor nucleotide. C–F Substrate binding modes in LpCdnE. The monoclinic crystal contains two protein molecules in an asymmetric unit. C, D One of them centered on the donor and acceptor nucleotides, respectively. E, F show another. G–J Binding modes of the substrate analog in LpCdnE. The orthorhombic crystal contains two protein molecules in an asymmetric unit. (G) and (H) show one of them centered on the donor and acceptor binding sites, respectively. I, J show another.