How Strongly Does Trehalose Interact with Lysozyme in the Solid State? Insights from Molecular Dynamics Simulation and Inelastic Neutron Scattering

Therapeutic proteins are usually conserved in glassy matrixes composed of stabilizing excipients and a small amount of water, which both control their long-term stability, and thus their potential use in medical treatments. To shed some light on the protein–matrix interactions in such systems, we performed molecular dynamics (MD) simulations on matrixes of (i) the model globular protein lysozyme (L), (ii) the well-known bioprotectant trehalose (T), and (iii) the 1:1 (in weight) lysozyme/trehalose mixture (LT), at hydration levels h of 0.0, 0.075, and 0.15 (in g of water/g of protein or sugar). We also supplemented these simulations with complementary inelastic neutron scattering (INS) experiments on the L, T, and LT lyophilized (freeze-dried) samples. The densities and free volume distributions indicate that trehalose improves the molecular packing of the LT glass with respect to the L one. Accordingly, the low-frequency vibrational densities of states (VDOS) and the mean square displacements (MSDs) of ly...