Vibrational Collective Dynamics of Dry Proteins in the Terahertz Region

Abstract

The coherent density fluctuations of a perdeuterated dry protein have been studied by Brillouin neutron spectroscopy. Besides a nearly wavevectorindependent branch located around 5 meV, a propagating mode with a linear trend at low wavevector Q is revealed. The corresponding speed of 3780 ± 130 m/s is definitely higher than that of hydrated proteins. Above Q = 0.8 Å −1 , this mode becomes overdamped, with lifetimes shorter than 0.1 ps, in fashion similar to glassy materials. The present results indicate that dry proteins sustain coherent density fluctuations in the THz frequency regime. The trend of the longitudinal modulus indicates that in this frequency range dry biomolecules are more rigid than hydrated proteins.

Coherent Neutron Scattering and Collective Dynamics in the Protein, GFP

“…In most cases only incoherent neutron scattering has been used (10,(27)(28)(29). A few studies utilizing inelastic x-ray scattering or higher energy neutron scattering on proteins have revealed some higher-frequency collective vibrational modes above the boson peak frequency (30,31). Coherent neutron scattering has also been applied to the analysis of domainlike motions in proteins on timescales of tens of nanoseconds (32)(33)(34), providing characteristic timescales and the amplitude of the domain motions and their changes upon ligand binding (33).…”

Future applications of the high-flux thermal neutron spectroscopy: the ever-green case of collective excitations in liquid metals

“…Despite the recent developments, deuteration remains a complex technique and the production of large sample quantities is still cost-and time-limited [206]. An estimate of the order of magnitude can be obtained by inelastic scattering experiments carried out on biological samples, like the dry maltose binding protein [207] where quantities of deuterated sample as large as 0.5 g were needed for a complete analysis of the dry protein dynamics. Actually, as discussed in [207], a considerable fast sound effect was observed (c 1 ¼ 3780 � 130 m/s at 2 THz versus an ordinary sound velocity c 0 ¼ 2000 � 30 m/s at 2 MHz) together with a second collective mode at 5 meV ' 1.21 THz resembling a similar excitation observed at 6 meV ' 1.45 THz in water.…”

“…An estimate of the order of magnitude can be obtained by inelastic scattering experiments carried out on biological samples, like the dry maltose binding protein [207] where quantities of deuterated sample as large as 0.5 g were needed for a complete analysis of the dry protein dynamics. Actually, as discussed in [207], a considerable fast sound effect was observed (c 1 ¼ 3780 � 130 m/s at 2 THz versus an ordinary sound velocity c 0 ¼ 2000 � 30 m/s at 2 MHz) together with a second collective mode at 5 meV ' 1.21 THz resembling a similar excitation observed at 6 meV ' 1.45 THz in water. A closer inspection of the 5 meV mode was possible thanks to incoherent neutron-scattering measurements on the hydrogenated counterpart of the dry protein, which provided the density of vibrational states of the system.…”

Using X-ray as a Probe of the Terahertz Dynamics of Disordered Systems – Complementarity with Inelastic Neutron Scattering and Future Perspectivess

“…However, nowadays, this interpretation needs some reconsideration because the L-T coupling was also observed in non-tetrahedral systems, such as glassy glycerol [54] and liquid metals [55][56][57][58][59]. Furthermore, a similar effect was reported in more complex systems such as binary mixtures [51] and biophysical samples [60][61][62].…”