Effect of water and polyols on the dynamics of lysozyme studied by solid-state NMR

One of the main goals of protein research is to understand the relationship between protein structure, dynamics, and function. The purpose of this dissertation is to investigate dynamic heterogeneity and the effects of water and polyols on dynamics and the dynamical transition in lysozyme using nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization mass spectrometry (ESI-MS).{09}; Both 13CH3-labeled and C 2H3-labeled lysozyme were investigated to explore dynamics at the protein surface. 13C CP-MAS solid state NMR spectra showed an improvement in spectral resolution on addition of water reflecting both a decrease in the distribution of isotropic chemical shifts, as preferred conformations are populated on hydration, as well as contributions from motional averaging of chemical shift anisotropy and dipolar coupling interactions. With increasing temperature and hydration, a change in 2H NMR spectral line shape was observed for lysine residues labeled with C 2H3 groups indicating the onset of a new motion at the melting point of water suggesting that the dynamic properties of protein surface groups are strongly coupled to those of the solvent.; In order to explore the dynamic heterogeneity of the protein interior, a solid-state 2H NMR study of a series of dry and hydrated lysozyme samples kinetically labeled by hydrogen isotope exchange so as to select regions of the protein interior with different isotope exchange rates has been conducted. Samples deuterated on the slowest exchanging sites or on the protein surface gave essentially the same line shape indicating that all peptide sites within the protein undergo the same type of motion with similar amplitudes. Interestingly, spin lattice relaxation times (T1 ) for the dry protein are found to correlate with the exchange rates of sites in the hydrated protein. Hydration leads to a significant decrease in T1 even for sites in the slow-exchange core. A mechanism involving small amplitude rigid-body fluctuations of the slow-exchange core within the plasticized protein matrix is proposed to explain this behavior.