Temperature Dependence of Confined Protein Hydration and Dynamics

The function and stability of proteins in water strongly depend on the temperature and conditions of the environment. The temperature dependence is thought to explain the denaturation of proteins at low and high temperatures, and the specific globular structure for protein function is determined by the hydrophobic effect. However, the strength of the hydrophobicity is strongly temperature dependent. Here, we have employed a very sensitive dielectric megahertz-to-terahertz frequency-domain spectroscopy system to probe lysozyme hydration shells and collective vibrational modes of lysozyme in water. Using the system, we explore the dielectric response of solvated lysozyme protein over a range of 50 MHz to 2 THz in a wide range of temperatures. The dielectric relaxation spectra reveal several polarization mechanisms at the molecular level with different time constants and dielectric strengths, reflecting the complexity of protein-water interactions. High-precision measurements of the hydration water and protein dynamics as a function of temperature provide the dynamical influence of protein on the temperature. Our results reveal critical information of protein dynamics and protein-water interfaces with temperature, which determine the biochemical functions and reactivity of proteins.