Global vibrational modes in proteins: Raman spectroscopy and numerical modeling

Protein biological functions are made possible by folding, a quick change in shape through which the protein reaches its functional three-dimensional structure. Understanding the mechanisms behind this complex phenomenon and how to direct it, will have an enormous influence in biology and medicine. Recent studies have attributed to mechanical vibrations that extend through the protein a crucial role in controlling structural conformational changes. For example, underdamped low-frequency (∼1011–1012 Hz) collective vibrational modes have been proposed as being responsible for efficiently directing biochemical reactions and biological energy transport. In this contribution we present the results of broad-range Raman spectroscopy measurements made on proteins in different forms, namely crystallized, powdered, and in solution. The use of ultra low frequency (ULF) filters allowed to observe vibrations around 1 THz (30 cm−1), as well as other peaks in the range 0–500 cm−1, that seem to be unassigned in the current literature. Those peaks could be associated to global and/or delocalized vibrational modes. Normal mode numerical calculations were performed on lattice models to investigate on such a possible correlation.