We further note that, in agreement with prior computational work, we did not obtain productive reaction trajectories for the analogous reaction through retention of configuration (Figures and, hypothesis 1). Visual examination of the resulting trajectories illustrates that for both pro-R and pro-S cleavage, the carboxylate that should be cleaved formed hydrogen bonds with multiple residues, including S76 of the dioxyanion hole (Figure ), which was prevalent with both conformers (above 50 % of the trajectory). Note that the non-reactive carboxylate group is placed in the dioxyanion hole. The observed hydrogen bonds can contribute to the stabilization of the substrate in the reactant state, disallowing the progress of the decarboxylation step, as both carboxylate groups are stabilized by a set of hydrogen bonding interactions, mimicking the corresponding non-enzymatic and uncatalyzed reaction in solution more closely, and likely leading to a very high reaction barrier for this process.