Intracellular Protein–Lipid Interactions Studied by Rapid-Scan Electron Paramagnetic Resonance Spectroscopy

Protein–membrane interactions play key roles in essential cellular processes; studying these interactions in the cell is a challenging task of modern biophysical chemistry. A prominent example is the interaction of human α-synuclein (αS) with negatively charged membranes. It has been well-studied in vitro , but in spite of the huge amount of lipid membranes in the crowded environment of biological cells, to date, no interactions have been detected in cells. Here, we use rapid-scan (RS) electron paramagnetic resonance (EPR) spectroscopy to study αS interactions with negatively charged vesicles in vitro and upon transfection of the protein and lipid vesicles into model cells, i.e. , oocytes of Xenopus laevis . We show that protein–vesicle interactions are reflected in RS spectra in vitro and in cells, which enables time-resolved monitoring of protein–membrane interaction upon transfection into cells. Our data suggest binding of a small fraction of αS to endogenous membranes.