Electron Attachment to DNA: The Protective Role of Amino Acids

TL;DR

This study investigates how amino acids influence electron attachment to DNA nucleobases, revealing a protective mechanism where amino acids shield nucleobases from damaging electrons and stabilize their anionic states.

Contribution

It introduces a detailed quantum chemical analysis of amino acid effects on DNA electron attachment, highlighting a shielding mechanism and stabilization of DNA's negative charge.

Findings

Amino acids facilitate a doorway mechanism for electron attachment to cytosine.

Higher amino acid concentrations shield nucleobases from incoming electrons.

Amino acids increase stability of nucleobase-bound anionic states, reducing damage.

Abstract

We have studied the effect of amino acids on electron attachment properties of DNA nucleobases, taking cytosine as a model system. The equation of motion coupled cluster theory with an extended basis set has been used to simulate the electron-attached state of the DNA model system. Four selected amino acids, Arginine, Alanine, Lysine, and Glycine which form a major component of histone proteins are considered to investigate their role in electron attachment to DNA nucleobase. The electron attachment to cytosine in all the cytosine-amino acid dimer complexes follows a doorway mechanism, where the electron gets transferred from initial dipole-bound doorway state to the final nucleobase-bound state through the mixing of electronic and nuclear degrees of freedom. In higher amino acid concentration, amino acid-bound state acts as the doorway state, where the initial electron density is localized on the amino acid, away from the nucleobase. This leads to the physical shielding of nucleobase from the incoming extra electron. At the same time, the presence of amino acids can increase the stability of nucleobase-bound anionic state, which can suppress the dissociative electron attachment induced sugar-phosphate bond breaking.