Study of the phase transition in lysozyme crystals by Raman spectroscopy

Background: Recently, 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 highfrequency vibrational modes arising from the protein and their temperature evolution in the vicinity of T-ph as well as on the detailed study of crystalline water dynamics near T-ph. Methods: Raman experiments have been performed at temperatures 295-323 K including T-ph. The lowfrequency modes and the modes of fingerprint region, CH-and OHstretching regions have been analyzed. Results and conclusions: In 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 T-ph. Pronounced changes in the dynamics of ethelixes and Tyr residues exposed on the protein surface point to the important role of Hbond rearrangements at the phase transition. Additionally the study of temperature evolution of OHstretching modes has shown an increase in distortions of tertahedral Hbond network of crystalline water above T-ph. These changes in water dynamics could play a crucial role in the mechanisms of the phase transition. General significance: The present results shed light on the mechanisms of the phase transition in lysozyme crystals. (C) 2015 Elsevier B.V. All rights reserved.