DNA heats up : Energetics of genome ejection from phage revealed by isothermal titration calorimetry

TL;DR

This study uses isothermal titration calorimetry to directly measure the heat released during DNA ejection from bacteriophage lambda, providing new thermodynamic insights into the process and confirming the role of DNA hydration.

Contribution

First direct calorimetric measurement of DNA ejection energetics from phage lambda, validating theoretical models and highlighting DNA hydration's role.

Findings

Heat release during DNA ejection measured directly.

Results align with previous models and simulations.

DNA hydration significantly influences genome confinement energetics.

Abstract

Most bacteriophages are known to inject their double-stranded DNA into bacteria upon receptor binding in an essentially spontaneous way. This downhill thermodynamic process from the intact virion toward the empty viral capsid plus released DNA is made possible by the energy stored during active packaging of the genome into the capsid. Only indirect measurements of this energy have been available until now using either single-molecule or osmotic suppression techniques. In this paper, we describe for the first time the use of isothermal titration calorimetry to directly measure the heat released (or equivalently the enthalpy) during DNA ejection from phage lambda, triggered in solution by a solubilized receptor. Quantitative analyses of the results lead to the identification of thermodynamic determinants associated with DNA ejection. The values obtained were found to be consistent with those previously predicted by analytical models and numerical simulations. Moreover, the results confirm the role of DNA hydration in the energetics of genome confinement in viral capsids.