The Theoretical Studies on Protein Microenvironment Regulating Active Hydrogen Transfer from Lysine Side Chain to Peptide Backbone

• 1、Chemistry and Chemical Engineering School ,Chongqing University,Chongqing 401331

Abstract：The mechanisms of the cleavage in peptide cation and protein induced by electron attachment have been a hot research recently. Specifically, the transfer of the corresponding active hydrogen can be explained by the proton-coupled electron transfer (PCET) mechanism. In this work, we systematically examine the roles of the different amino acid side chains in modulating active hydrogen transfer from the ammonium group of the protonated lysine side chain to the oxygen atom of neighbor amide carbonyl in the peptide backbone using B3LYP/6-31+G (d, p) method. To analyze the structures of the reactants, transition states and products with the corresponding spin density distributions and the activation energies, we reveal that active hydrogen migration in all optimized stable peptide models takes place via a proton-coupled Rydberg-state electron transfer（PCRET）mechanism with proton transfer from the ammonium group of the lysine to a O-atom of nearby backbone amide and at the same time electron transfer through Rydberg orbital. In these reactions, the push-pull effect of the side chains of different amino acids can reduce or increase the activation energies and then regulates the rate of active hydrogen transfer.

Keywords： protein microenvironment, side chain of lysine, active hydrogen, proton-coupled electron transfer