A solid-state NMR study of protein mobility in lyophilized protein-sugar powders

The molecular mobility of protein in lyophilized lysozyme-sugar systems stored at different relative humidities was studied using solid-state NMR. Relaxation measurements, T(1) of high-frequency (MHz), and T(1rho), of low-frequency (kHz) motions, were performed on lysozyme lyophilized with lactose and trehalose. Molecular aggregation and enzymatic activity of the protein were determined using HPLC and bioassays. An increase in hydration had little effect on the T(1rho) values of pure lysozyme, trehalose, lactose, trehalose-lysozyme, and lysozyme at low lactose concentrations. The T(1) values of pure sugar increased as moisture content increased. The presence of both sugars led to increased T(1) values of the lysozyme but increasing hydration gradually reduced T(1) values. When a larger amount of lactose was lyophilized with lysozyme, longer T(1) (and T(1rho)) values were seen for lactose than for lysozyme. Although longer T(1) values were related to an increase in protein stability, the effect of crystallization and sugar type appeared to be major contributing factors. Trehalose and lactose decreased relaxation rates in the lysozyme-sugar systems while hydration increased relaxation rates that were correlated with changes in aggregation and activity of the protein.