Effect of Me2SO on Membrane Phase Behavior and Protein Denaturation of Human Pulmonary Endothelial Cells Studied by In Situ FTIR Spectroscopy

Abstract

Fourier transform infrared spectroscopy (FTIR) provides a unique technique to study membranes and proteins within their native cellular environment. FTIR was used here to study the effects of dimethyl sulfoxide (Me2SO) on membranes and proteins in human pulmonary endothelial cells (HPMECs). Temperature-dependent changes in characteristic lipid and protein vibrational bands were identified to reveal the effects of Me2SO on membrane phase behavior and protein stability. At Me2SO concentrations equal to or below 10% (v/v), Me2SO was found to decrease membrane conformational disorder. At higher Me2SO concentrations (15% v/v), however, membrane conformational disorder was found to be similar to that of cells in the absence of Me2SO. This effect was observed over a wide temperature range from 90°C down to −40°C. Me2SO had no clear effects on cellular proteins during freezing. During heating, however, Me2SO had a destabilizing effect on cellular proteins. In the absence of Me2SO, protein denaturation started at an onset temperature of 46°C, whereas at 15% Me2SO the onset temperature of protein denaturation decreased to 32°C. This implies that in the presence of Me2SO the onset temperature of protein denaturation is lower than the normal growth temperature of the cells, which could explain the well documented toxic effect of Me2SO at physiological temperatures. Me2SO destabilizes cellular proteins during heating and decreases membrane conformational disorder over a wide temperature range.