Terahertz vibration and resonance phenomena in proteins

Protein dynamics is strictly connected with protein biological function. In fact, the directions of the largest thermal fluctuations of the structure of a protein in its native state are the directions of its low-frequency modes (below 1 THz); these modes are named acoustical modes by analogy with the acoustical phonons of a material. The acoustical modes of a protein assist its conformational changes (folding) and are related to its biological functions [1,2]. In Mechanics it is known that instability of an equilibrium configuration of an elastic system may be favoured by resonant oscillations. Therefore, we cannot exclude that large conformational changes in proteins may occur as the result of nano-instabilities induced, or favoured, by resonant mechanical oscillations: we shall think that the right stimuli at the right frequencies could cause changes in the 3D structure, and consequences of that are all to be discovered. In [3] the authors investigated experimentally (by Raman spectroscopy) and numerically (by normal-mode calculations) low-frequency vibrations in lysozyme. In [4] they presented Raman spectra obtained on lyophilized and rehydrated powder samples of sodium-potassium pump (Na+/K+-ATPase), focusing the attention on unassigned low-frequency peaks. Finally, in [5] the authors performed normal-mode calculations on the Na/K-ATPase crystal structure, obtaining information on low frequency modes that helped in interpreting the experimental results in [4]. Based on the results of their previous studies, the authors planned a new experimental campaign where a latest-generation THz beamline is used to excite resonant vibrations in proteins by THz photons, using ultra-short, coherent, powerful pulses. The results of this recent study are presented in this contribution