Base-catalyzed peptide hydrolysis is insensitive to mechanical stress

Biochemical reactions can be guided by mechanical stress. An external force has been previously shown both experimentally and theoretically to act as a catalyst for the scission of a disulfide bond in thiol/disulfide exchange reactions. How the dynamics of peptide hydrolysis, one of the most prevalent biochemical reactions, is influenced by a stretching force was investigated here using combined quantum and molecular mechanical (QM/MM) simulations together with transition path sampling. Our simulations predict mechanical force to only marginally enhance the reactivity of the rate-limiting step, the nucleophilic attack of hydroxide to the peptide moiety, and not to alter the reaction mechanism, even though the peptide bond and its electron conjugation is weakened by force. We describe a previously unidentified hydrogen bonded intermediate state, which is likely to play a role in general in base-catalyzed and analogous enzymatic reactions. Our predictions can be directly tested by single molecule stretching experiments.