Figure 2.

(a) The LigL structure (PDB code 4yai; Pereira et al., 2016 ▸) was solved at 1.6 Å resolution with two molecules per asymmetric unit, which represents the biological dimer, showing Mg²⁺ was essential for the crystal lattice contacts. A twofold (C2) symmetry axis is shown with a solid oval symbol. (b) A 2mF _o–DF _c electron density map for the LigL structure contoured at 1.5σ is shown in blue around the Mg²⁺ ions, the water molecules, and the side chains of Glu73 and Glu77. The octahedral coordination of Mg²⁺ is water mediated by the negative surface residues Glu73 and Glu77, generating the major crystal contact between symmetry-related molecules. Water molecules are shown as red spheres.