Label-free surface-enhanced Raman spectroscopy of lipid-rafts from hepatocyte plasma membranes

Lipid rafts are sphingomyelin/cholesterol-rich domains present in the plasma membrane of eukaryotic cells. In the hepatocyte, it has been shown that these domains intervene and modify a wide range of functions from which cell signaling in health and disease is of major importance. The present investigation proposes a novel strategy for the study of plasma membrane lipid rafts using surface-enhanced Raman spectroscopy (SERS) and spectra processing employing the principal component analysis (PCA) in correlation with conventional biochemical techniques. SERS has been used for artificial membranes; our approach has the advantage that allows studying purified biological membranes using small volumes of biological samples and a very simple protocol. Therefore, the use of SERS/PCA represents an important advantage for the study not only of the structure and composition of biological membranes but also for the understanding of the functions carried by the membrane-embedded proteins. Our work using SERS/PCA for the first time shows a correlation when studying the composition of lipid rafts from the cell plasma membrane and the catalytic activity of the Ca2+-ATPase, and its direct association with the presence of specific lipids located in membrane lipid rafts. Also, we show that changes in plasma membrane and the catalytic activity of the Ca2+-ATPase activity present in the plasma membrane of hepatocytes after partial depletion of membrane cholesterol carried out by methyl-beta-cyclodextrin correlate with the changes in the enzyme activity and the presence of cholesterol-rich domains of lipid rafts. Copyright (c) 2017 John Wiley & Sons, Ltd.