Fig. 2. OB forms a covalent bond with the Tyr462 residue of ThrRS.

a The catalytic center of ThrRS with bound OB. The phenolic group of Tyr462 (green sticks) forms a new ester bond with OB (orange sticks). The linkage atoms of the original 4-membered ring in OB are indicated by red stars. Interacting residues are shown as sticks. The 2Fo-Fc electron density of Tyr462-OB (contoured at 1.0 σ) is shown as a gray transparent surface. b Close-up view of residues coordinating with a Zn²⁺ ion. Two hydroxyl groups on the o-diphenol moiety of OB coordinate with a Zn²⁺ ion. Residues Cys334, His385, His511, Tyr462, and OB are shown as sticks. The 2Fo-Fc electron density of these residues (contoured at 1.0 σ) is shown as a transparent surface. c Schematic illustration of the covalent bond formation between ThrRS (Tyr462) and OB.