Key configurations for step 1, the nucleophilic attack by Oγ atom of Ser117. The geometries were optimized at QM/MM(B3LYP/6-31G*:AMBER) level. The key distances in the figure are in angstroms. Carbon, oxygen, nitrogen, and hydrogen atoms are colored in green, red, blue, and white, respectively. The backbone of the protein is rendered as a cartoon and colored in orange. The QM atoms are represented as ball and stick, and the surrounding residues rendered as stick. The figures below are represented using the same method.