Dielectric Behavior of Lysozyme and Ferricytochrome-c in Water/Ethylene-Glycol Solutions

Abstract

This work deals with a dielectric study at radio frequencies of the influence at room temperature of two organic molecules, known as cryo-protectants, ethylene-glycol and glycerol, on conformational and dynamic properties of two model proteins, lysozyme (lys) from chicken egg-white and ferricytochrome-c (cyt-c) from horse heart. Cyt-c is a compact globular protein whereas lys is composed of two structural domains, separated by the active site cleft. Measurements were carried out at the fixed temperature of 20 degrees C varying the concentration of the cosolvent up to 90% w/w. From the analysis of the dielectric relaxation of the protein solution, the effective hydrodynamic radius and the electric dipole moment of the protein were calculated as a function of the cosolvent concentration. The data show that glycerol does not modify significantly the conformation of both proteins and cyt-c is also stable in the presence of ethylene-glycol. On the contrary ethylene-glycol strongly affects the dielectric response of lysozyme denoting a specific effect on its conformation and dynamics. The data are coherently interpreted hypothesizing that glycol molecule wedges between and separates the two domains of lys making them rotationally independent.

Interactions between single-walled carbon nanotubes and lysozyme

“…In fact, protein concentration is too low to give any dielectric response. In addition, the observed relaxation frequency in the present systems (below 1 MHz) is not compatible with the dielectric relaxation pertinent to the protein, which occurs at frequencies around 10 MHz [32,33]. The reported dielectric behavior is typical of charged colloids and may be ascribed to the polarization of counter-ions in the double layer around nanotubes [40,41].…”

“…Very presumably, the above trends imply changes in the electrical double layer thickness surrounding the complexes. The effect has not direct links with similar phenomena occurring on pure aqueous lysozyme, whose dielectric relaxation frequency occurs at much higher values (around 10 MHz) [32,33]. In addition, no overlapping of the two relaxation modes can be observed in the plots.…”

Lysozyme binding onto cat-anionic vesicles

“…Above 0.20 mmol L −1 in protein ε progressively increases, while f * values remain nearly constant at about 9 MHz. This value corresponds to the relaxation time for the orientational polarization of molecularly dispersed lysozyme in water [46], and does not change with the free protein content. Binding saturation occurs at the inflection point of ε vs [LYSO] plots, where relaxation processes pertinent to free LYSO are observed.…”

A comparison of the activation energy of viscous flow for hen egg-white lysozyme obtained on the basis of different models of viscosity for glass-forming liquids

“…It serves as a model protein for different biophysical and biochemical studies. Structure, dynamics and hydration of HEWL have been studied by a wide range of experimental techniques such as NMR spectroscopy (Smith et al, 1993;Gregory et al, 1993;Diakova et al, 2007;Baranowska & Olszewski, 1996), dielectric spectroscopy (Miura et al, 1994;Bonincontro et al, 2004;Knab et al, 2006;English et al, 2009;Woods, 2010), Fourier transform infrared spectroscopy (Hadden et al, 1995;Turula & de Haseth, 1996), X-ray crystallography (Yagi et al, 2009), neutron scattering (Lushnikoy et al, 2009), circular dichroism (Maroufi et al, 2008) and viscometry (Monkos, 1997). Theoretical treatment of those problems one can also find in the literature (Zhou, 1995;Roth et al, 1996).…”