Isothermal Titration Calorimetry Measures Energy of Viral Infection

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Scientists from Carnegie Mellon University, Lund University in Sweden, and Universite de Lyon in France have for the first time measured the energy released when a virus injects its DNA into the host. In this case it was a double standed bacteriophage lambda that infected a bacterium with its DNA, but the technique, called isothermal titration calorimetry (ITC), and knowledge derived from it can be applied to other virus types.

Many viruses, whether they infect bacteria, plants or animals, are adept at packing long stretches of nucleic acid (DNA or RNA) within their nanometer-sized protein shells. In many of the viruses that contain double-stranded DNA, the DNA gets packaged so tightly that it bends upon itself, resulting in repulsive forces that exert a tremendous amount of pressure on the virus's outer shell, indicating a great amount of stored energy. At the moment of infection, when the DNA is being shot out of the virus, the energy stored in the tightly packed DNA is released and converted into thermal energy.

Evilevitch [Alex Evilevitch, physicist at CMU] used ITC to measure the thermal energy released during genome ejection, which is the same as the stored internal energy that results from genome packaging. His results, which agree with analytical models and computer simulations, show that the heat released increases as DNA length increases. He also discovered that the ordering of water molecules around DNA strands inside the virus (called hydration entropy) has a tremendous influence on the build up of energy. This unpredicted effect was not accounted for in the previous models.

Press release: Carnegie Mellon Physicist the First To Measure Energy Released From a Virus During Infection ...

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