Studies of the translational entropy contribution to protein stability by use of the HIV-1 protease as a model system

In the quest to predict the Gibbs energy of protein stability, the magnitude of the translational entropy contribution to the stability of 2-state oligomeric proteins has yet to be agreed upon by any meaningful consensus of the various research groups engaged in the task. In an effort to resolve the ongoing dispute, the work herein describes the use of the HIV-1 protease as a model system with which to quantitatively compare and contrast the translational entropy contribution predicted by the cratic and Sackur-Tetrode methodologies versus the experimentally observed value. Toward this end, Differential Scanning Calorimetry was used to measure the stability of wild-type dimeric HIV-1 protease and a series of tethered HIV-1 proteases. The difference in stability and total entropy of unfolding is shown to agree within 0.6 +/- 2.0 cal K -1 mol-1 of that which is predicted by the cratic methodology for the reversible 2-state unfolding of a dimeric protein.