Sub-terahertz spectroscopy reveals that proteins influence the properties of water at greater distances than previously detected

Abstract

Erratum: "Sub-terahertz spectroscopy reveals that proteins influence the properties of water at greater distances than previously detected" [J. Chem. Phys. 142, 055101 (2015) The initial purpose of the study is to systematically investigate the solvation properties of different proteins in water solution by terahertz (THz) radiation absorption. Transmission measurements of protein water solutions have been performed using a vector network analyser-driven quasi-optical bench covering the WR-3 waveguide band (0.220-0.325 THz). The following proteins, ranging from low to high molecular weight, were chosen for this study: lysozyme, myoglobin, and bovine serum albumin (BSA). Absorption properties of solutions were studied at different concentrations of proteins ranging from 2 to 100 mg/ml. The concentration-dependent absorption of protein molecules was determined by treating the solution as a two-component model first; then, based on protein absorptivity, the extent of the hydration shell is estimated. Protein molecules are shown to possess a concentration-dependent absorptivity in water solutions. Absorption curves of all three proteins sharply peak towards a dilution-limit that is attributed to the enhanced flexibility of protein and amino acid side chains. An alternative approach to the determination of hydration shell thickness is thereby suggested, based on protein absorptivity. The proposed approach is independent of the absorption of the hydration shell. The derived estimate of hydration shell thickness for each protein supports previous findings that protein-water interaction dynamics extends beyond 2-3 water solvation-layers as predicted by molecular dynamics simulations and other techniques such as NMR, X-ray scattering, and neutron scattering. According to our estimations, the radius of the dynamic hydration shell is 16, 19, and 25 Å, respectively, for lysozyme, myoglobin, and BSA proteins and correlates with the dipole moment of the protein. It is also seen that THz radiation can serve as an initial estimate of the protein hydrophobicity. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx

Time-Domain THz Spectroscopy Reveals Coupled Protein–Hydration Dielectric Response in Solutions of Native and Fibrils of Human Lysozyme

“…Under these assumptions the resultant average dipole moment induced over the solution, and hence the THz absorption, is further reduced. Previous measurements of proteins (including lysozyme) in water solutions have, however, shown that rather than the THz absorption being lower than expected when considering only water removal, the THz absorption is actually higher [24][25][26][27][28][29], consistent with the results reported here (Fig. 2).…”

“…However, when lower concentrations are used, terahertz techniques suggest that the population of hydration water is much larger and extends over multiple layers. Extended hydration shells, where the effect of the protein on the water molecules is evident, have been reported to vary between 15 Å and 25 Å from the solute surface for different proteins [25][26][27][28][29]. While these works are based on the simplistic assumption that the absorption coefficient of a complex system can always be written as the weighted sum of the absorption of its components [35], here we show how determining the complex dielectric response provides a much more informative and reliable assessment of the impact of protein-water interactions on the water environment.…”

Modulation of the Hydration Water Around Monoclonal Antibodies on Addition of Excipients Detected by Terahertz Time-Domain Spectroscopy

“…In this context, it is important to keep in mind that the magnitude of the extent of the hydration shell is sensitive to the frequency that is used to calculate its value. In this work we have fixed the frequency to 1 THz, whereas other groups have used frequencies between 0.2 and 2.5 THz for similar analysis . In this frequency range, the terahertz spectra exhibit losses because of the structural dielectric relaxations (these contributions decrease with frequency) as well as librational/vibrational motions (increasing losses with frequency) .…”

Biomedical Applications of Terahertz Spectroscopy and Imaging

“…Due to its distinctive spectral responses to THz radiation, the dynamic hydration shell can be precisely determined by probing protein-induced fast solvation dynamics by THz spectroscopy [4]. A broader hydration shell than previously determined by molecular dynamics simulations has been detected by THz spectroscopy, highlighting its potential for estimating protein hydrophobicity [28]. In addition, the protein-ligand binding between hen egg white lysozyme (HEWL) and triacetylglucosamine (3NAG) was successfully probed at 270 K [29], showing that HEWL + 3NAG has smaller absorption coefficients than free HEWL ( Figure 2C) and proving the feasibility of monitoring protein-ligand binding in solution using THz spectroscopy.…”