Study of the phase transition in lysozyme crystals by Raman spectroscopy

BackgroundRecently, it has been revealed that tetragonal lysozyme crystals show a phase transition at 307 K upon heating. The underlying mechanisms of the phase transition are still not fully understood. Here we focus on the study of high-frequency vibrational modes arising from the protein and their temperature evolution in the vicinity of Tph as well as on the detailed study of crystalline water dynamics near Tph.MethodsRaman experiments have been performed at temperatures 295–323 K including Tph. The low-frequency modes and the modes of fingerprint region, CH- and OH-stretching regions have been analyzed.Results and conclusionsIn spite of the absence of noticeable rearrangements in protein structure, the high-frequency vibrational modes of lysozyme located in the fingerprint region have been found to exhibit the features of critical dynamics near Tph. Pronounced changes in the dynamics of α-helixes and Tyr residues exposed on the protein surface point to the important role of H-bond rearrangements at the phase transition. Additionally the study of temperature evolution of OH-stretching modes has shown an increase in distortions of tertahedral H-bond network of crystalline water above Tph. These changes in water dynamics could play a crucial role in the mechanisms of the phase transition.General significanceThe present results shed light on the mechanisms of the phase transition in lysozyme crystals