Thermodynamic Properties Underlying the α-Helix-to-β-Sheet Transition, Aggregation, and Amyloidogenesis of Polylysine as Probed by Calorimetry, Densimetry, and Ultrasound Velocimetry

In this work, we performed a detailed thermodynamic study of an aggregation-prone polypeptide, polylysine, to gain a deeper insight into the scenario of physicochemical events during its unfolding, aggregation, and amyloidogenesis. The precise and simultaneous determination of the partial molar volume, the heat capacity, and the coefficients of thermal expansion, as well as adiabatic and isothermal compressibility of the protein upon unfolding and aggregation, yields a thermodynamic picture of the aggregation process highlighting the importance of volume fluctuations during unfolding and amyloidogenesis of proteins.