Hydration structure analysis of lysozyme amyloid fibrils by thermally stimulated depolarization currents (TSDC) technique

Maria Grazia Bridelli,Rosanna Capelletti

doi:10.1155/2008/793491

Abstract

Thermally stimulated depolarization currents technique has been employed to investigate the conformation of hen egg white lysozyme in native and amyloid form, in the state of powder at very low hydration level. The technique, able to detect the current generated by thermally activated reorientation of water dipoles previously oriented by an electric field, exploits H2O dipoles, belonging to the solvation shell, as a probe to gain information on the protein conformation.Large differences are detected between the TSDC spectra related to the two different protein conformations, for what concerns the number and position of the main peaks, the native form displaying two peaks, atTM=175 K and atTM=297 K, and the amyloid one, only one at intermediate temperature (TM=235 K). The spectra have been compared with those monitored for poly-L-lysine (MW 80400), as received and prepared in different ways, i.e.α-helix,β-sheet, and coil conformation, respectively. The poly-L-lysine spectra show specific features that can be attributed to water texture around the secondary structure adopted by the macromolecule: the results stress how TSDC technique is a tool of great potential value in the conformational analysis of proteins.

Highlights

It is well known that protein molecules are surrounded in the cell by a hydration shell formed by interacting water molecules
thermally stimulated depolarization currents (TSDC) spectrum of native form lysozyme is shown in Fig. 1
The spectrum is similar to those appeared in literature in the past [2,14], it consists of two main peaks: a weak one at TM = 175 K, which can be labeled low temperature (LT) peak, and a strong one at TM = 297 K, high temperature (HT) peak

Summary

Introduction

It is well known that protein molecules are surrounded in the cell by a hydration shell formed by interacting water molecules. The shell is not a continuous network of water molecules but is made up of patches locally distributed in dependence of the heterogeneous surface chemistry or occluded in the internal cavities. They are oriented by the surface properties of the protein and are named “bound” molecules, due to the restricted motions with respect to water molecules in pure bulk: ordering changes may indicate structural or conformational differences among macromolecules. The bound water limited mobility allows molecule reorientation, and can be described in term of relaxation times. Different relaxation times can be distinguished by using the thermally stimulated depolarization currents (TSDC) technique. TSDC technique was applied in the past to a variety of natural and synthetic biopolymers and has provided a valuable contribution to the understanding of the complex behaviour of the structured wa-

Objectives

Methods

Results