Single-molecule derivation of salt dependent base-pair free energies in DNA

TL;DR

This study introduces a novel single-molecule unzipping technique to accurately measure DNA base-pair free energies and salt effects, improving thermodynamic predictions over traditional bulk methods.

Contribution

It provides a new method combining mechanical unzipping, physical modeling, and optimization to determine DNA free energies and salt corrections with high precision.

Findings

Measured 10 base-pair free energies with 0.1 kcal/mol accuracy

Identified salt correction values specific to base pairs

Enhanced prediction accuracy for DNA unzipping forces and melting temperatures

Abstract

Accurate knowledge of the thermodynamic properties of nucleic acids is crucial to predicting their structure and stability. To date most measurements of base-pair free energies in DNA are obtained in thermal denaturation experiments, which depend on several assumptions. Here we report measurements of the DNA base-pair free energies based on a simplified system, the mechanical unzipping of single DNA molecules. By combining experimental data with a physical model and an optimization algorithm for analysis, we measure the 10 unique nearest-neighbor base-pair free energies with 0.1 kcal mol-1 precision over two orders of magnitude of monovalent salt concentration. We find an improved set of standard energy values compared with Unified Oligonucleotide energies and a unique set of 10 base-pair-specific salt-correction values. The latter are found to be strongest for AA/TT and weakest for CC/GG. Our new energy values and salt corrections improve predictions of DNA unzipping forces and are fully compatible with melting temperatures for oligos. The method should make it possible to obtain free energies, enthalpies and entropies in conditions not accessible by bulk methodologies.