Deconstructing protein phase diagrams
In the process of coming up with new exam questions for my undergraduate thermodynamics and condensed matter course I came across the following pressure-temperature phase diagram for the protein ribonuclease A at pH 2.0. It is taken from a 1995 Biochemistry paper and I came across it in the wonderful text by Dill and Bromberg. [Aside: I wondered if the water freezing was an issue but all along the curve the solvent water is liquid because dP/dT is negative for the liquid-solid line of pure water]. Natural scientific questions are: What are the mechanisms of "cold" and pressure-induced denaturation? What are the associated changes in protein structure? Is this a generic type of phase diagram for proteins? What role does water and hydrophobic interactions play? A nice review article from 2002 by Smeller discusses how these diagrams are indeed generic and their shape can be understood in terms of a simple thermodynamic theory due to Hawley in 1971. One simply expand