FIGURE 4.
ES*-acylation structure shows His-166 adopting flipped-out conformation and confirms Lys-73 as general base for acylation. a, active site in the ES*-acylation structure. Fo − Fc omit map (purple) is drawn in mesh format and contoured at 2.0 σ. The dashed lines indicate hydrogen bonds. b, superposition of ES*-acylation (cyan) and apo structures (green). Dashed lines mark the H-bonds. The flipped-out conformation of E166H is marked with an arrow. The tilting of Lys-73 is marked by Lys-73–Ser-130 H-bond. c, scheme of the proposed proton transfer from Lys-73 to His-166 during the acylation step and the resulting “flipped-out” conformation of His-166.