The Melting Diagram of Protein Solutions and Its Thermodynamic Interpretation.

Péter Tompa,Kálmán Tompa,Mónika Bokor

doi:10.3390/ijms19113571

Abstract

Here we present a novel method for the characterization of the hydration of protein solutions based on measuring and evaluating two-component wide-line 1H NMR signals. We also provide a description of key elements of the procedure conceived for the thermodynamic interpretation of such results. These interdependent experimental and theoretical treatments provide direct experimental insight into the potential energy surface of proteins. The utility of our approach is demonstrated through the examples of two proteins of distinct structural classes: the globular, structured ubiquitin; and the intrinsically disordered ERD10 (early response to dehydration 10). We provide a detailed analysis and interpretation of data recorded earlier by cooling and slowly warming the protein solutions through thermal equilibrium states. We introduce and use order parameters that can be thus derived to characterize the distribution of potential energy barriers inhibiting the movement of water molecules bound to the surface of the protein. Our results enable a quantitative description of the ratio of ordered and disordered parts of proteins, and of the energy relations of protein–water bonds in aqueous solutions of the proteins.

Highlights

Wide-line 1H NMR is an accepted method to delineate the structures of hydrogen-containing molecules determined primarily by X-ray and, to a lesser extent, by neutron-scattering
Here we present a novel method for the characterization of the hydration of protein solutions based on measuring and evaluating two-component wide-line 1H NMR signals
Perhaps it is not unnecessary to repeat that the amplitude value of the slow component of the measured free-induction decay (FID) signal extrapolated to t = 0 gives directly the number n of resonant protons, whereas the temperature dependence of MD gives the dependence of n on thermal excitation energy

Summary

Introduction

Wide-line 1H NMR is an accepted method to delineate the structures of hydrogen-containing molecules determined primarily by X-ray and, to a lesser extent, by neutron-scattering This way, it can provide information on the location and structural environment of hydrogen atoms in proteins. We have previously reviewed relevant features of this approach in our works “Hydrogen skeleton, mobility and protein architecture” [1] and “Studying molecular motions in solid states by NMR” [2]. Based on these studies, we state that molecular motions in the sample result in narrowing of the wide-line NMR spectrum. Our goal is to advance from this observation to arrive at the thermodynamic characterization of protein systems

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Results

Conclusion