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

Abstract

Here we reveal details of the interaction between human lysozyme proteins, both native and fibrils, and their water environment by intense terahertz time domain spectroscopy. With the aid of a rigorous dielectric model, we determine the amplitude and phase of the oscillating dipole induced by the THz field in the volume containing the protein and its hydration water. At low concentrations, the amplitude of this induced dipolar response decreases with increasing concentration. Beyond a certain threshold, marking the onset of the interactions between the extended hydration shells, the amplitude remains fixed but the phase of the induced dipolar response, which is initially in phase with the applied THz field, begins to change. The changes observed in the THz response reveal protein-protein interactions mediated by extended hydration layers, which may control fibril formation and may have an important role in chemical recognition phenomena.

Terahertz absorption of lysozyme in solution

“…In contrast to this prediction, simulations 27,31 and absorption measurements for hydrated lysozyme 32 and for some amino acids 18 have suggested that the polarization of the interface can significantly deviate from the Maxwell scenario. We indeed show below that the so-called Lorentz void, 33 instead of the Maxwell void (Eq.…”

“…The experimental data 32 for the absorption coefficient of lysozyme were obtained by averaging absorption over the interval of frequencies 0.38 − 0.92 THz. There is therefore a sufficient frequency overlap between the data for bulk water 40 and solutions.…”

“…There is therefore a sufficient frequency overlap between the data for bulk water 40 and solutions. 32 The refractive index of the protein, n p ≃ 1.55, is from Ref. 50.…”

Solvent dynamics play a decisive role in the complex formation of biologically relevant redox proteins

“…the hydration shell, have a distinct absorption which differs from bulk water, consistent with previous studies of proteins in solution. 18,36,37,39 However, the manner in which water interacts with the two proteins is different, evidenced by the opposite behavior in a avg . Coupling of water to the protein depends upon its surface properties, in which the local topography influences interactions with water.…”

Towards Intense THz Spectroscopy on Water: Characterization of Optical Rectification by GaP, OH1, and DSTMS at OPA Wavelengths

“…OR typically allows us to generate intense THz radiation below 5 THz (sketched in light green and light red in Figure 1c), while DFG covers higher frequencies (dark green and dark red in Figure 1c). Both inorganic (LiNbO 3 [66][67][68][69][70][71][72][73][74][75][76][77], GaSe [78][79][80], ZnTe [81,82], LiGaS 2 [83], GaP [84][85][86][87][88][89]) as well as organic (DSTMS [89][90][91][92], OH1 [93][94][95][96][97], DAST [98,99], DPFO [100], HMQ-TMS [101], OHQ-N2S [102]) crystals are phase-matched in the NIR and can emit pulsed THz fields with peak amplitudes in excess of 1 MV/cm. The approximate spectrum of the strongest THz pulses generated to date by non-linear optical methods in inorganic [62,64] and organic [63,65] crystals are shown in green and in red in Figure 1c, respectively.…”