Abstract

Introduction K-peptide (GILQINSRW) – short 9 amino acid fragment of the hen egg white lysozyme has the ability to form amyloid structures. Dimethyl sulfoxide (DMSO) is an osmolyte which can alter this ability. Our goal was to get an insight into the mechanism of Kpeptide-DMSO interactions in aqueous solutions. Such a knowledge can be helpful to understand processes leading to various neurodegenerative diseases. Methods ATR-FTIR spectroscopy (Thermo Nicolet 8700 equipped with single reflection diamond cell GoldenGate ATR accessory) was used to analyse interactions between solutes in their different proportions: the concentration of DMSO was kept constant in each solution while the peptide concentration varied. In addition, DSC calorimetry (nanoDSC, Thermo) allowed to determine thermal stability of the Kpeptide in aqueous solution with or without the addition of DMSO in the wide temperature range: 10-100 oC. Results The IR spectrum of the K-peptide exhibited a very strong peak usually attributed to beta-sheets. However, its shape was clearly different than in the case of other native or even denatured proteins. We assumed that it was due to the presence of a specific sheets of amyloid structures. The experimental design allowed to observe changes in relatively sharp peaks on ATR-FTIR spectra attributed to chemical bonds of DMSO caused by the presence of the peptide. These changes turned out to be weak, yet DSC calorimetry allowed to conclude that the K-peptide undergoes a few structural changes during the heating process. Depending on the solution composition and protein concentration, the number and exact temperatures of these transitions varied. Acknowledgements This work was funded by the National Science Centre, Poland (grant 2017/26/D/NZ1/00497).

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