Modelling proton tunnelling in the adenine-thymine base pair

Area of Science:

• Computational chemistry
• Quantum mechanics
• Molecular dynamics

Background:

• Adenine-thymine base pairs are fundamental to DNA structure and function.
• Tautomerization of DNA bases can lead to mutations.
• Understanding the mechanisms of tautomerization is crucial for molecular biology.

Purpose of the Study:

• To investigate the role of quantum tunneling in adenine-thymine (A-T) base pair tautomerization.
• To calculate the potential energy surface and barrier heights for A-T tautomerization.
• To assess the influence of environmental factors, like water molecules, on proton transfer.

Main Methods:

• Density functional theory (DFT) was used to calculate the energies of canonical and tautomeric A-T forms.
• Transition state searches determined the reaction pathway and potential energy surface.
• The time-dependent master equation, including a dissipative Lindblad term, modeled quantum tunneling and environmental effects.

Main Results:

• Quantum tunneling is improbable as a significant mechanism for A-T tautomer formation.
• The calculated tunneling probability, even with environmental coupling, reached a maximum of 2 × 10⁻⁹.
• Variations in wave function or potential energy surface geometry minimally impacted tunneling probability.

Conclusions:

• Proton transfer via quantum tunneling is not a likely driver for adenine-thymine tautomerization in DNA.
• The study provides quantitative insights into the limitations of quantum tunneling in this biological context.
• Further research may explore alternative mechanisms for DNA base pair alterations.