Fig. 2. Processes of acylation with the minimal active site assembly.

a Initial structure of OtCE15A and MeGlcA constructed based on in silico esterification of GlcA complex of OtCE15A (based on PDB 6SYR). c Relevant TI1 state to describe the reaction in acylation. b, d Corresponding relevant free-energy profiles generated from QM/MM simulations. Carbon atoms of MeGlcA and the catalytic triad, i.e., Ser267, Glu290, and His408 in the QM area are shown in green and cyan, respectively. For clarity, some hydrogen atoms in the QM area, the counterions and water molecules are not shown, here and in the forthcoming figures. There are a total of 48 atoms in the QM area, and the charge is −1. d₁ denotes the distance between the hydroxyl proton of Ser267 and Nε of His408. d₂ denotes the distance between the proton of the Nε of His408 and O of the ester in MeGlcA. Data are presented as mean values ± the standard error inferred from three independent runs. Source data for b, d are provided as a Source Data file.