Proton transfer in guanine-cytosine base pairs in b-DNA

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Chemical Theory and Computation, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.jctc.9b00757A double proton transfer reaction in a guanine-cytosine (GC) base pair has been proposed as a possible mechanism for rare tautomer (G*C*) formation and thus a source of spontaneous mutations. We analyze this system with free energy calculations based on extensive Quantum Mechanics/Molecular Mechanics simulations to properly consider the influence of the DNA biomolecular environment. We find that, although the G*C∗ rare tautomer is metastable in the gas phase, it is completely unstable in the conditions found in cells. Thus, our calculations show that a double proton reaction cannot be the source of spontaneous point mutations. We have also analyzed the intrabase H transfer reactions in guanine. Our results show that the DNA environment gives rise to a large free energy difference between the rare and canonical tautomers. These results show the key role of the DNA biological environment for the stability of the genetic codeThis work was supported by Grants No. MAT2017-88258-R and MDM-2014-0377 (María de Maeztu Programme for Units of Excellence in R&D) from the Ministerio de Economía Industria y Competitividad (Spain