Tensing Flipper: Photosensitized Manipulation of Membrane Tension, Lipid Phase Separation, and Raft Protein Sorting in Biological Membranes

The lateral organization of proteins and lipids in the plasma membrane is fundamental to regulating a wide range of cellular processes. Compartmentalized ordered membrane domains enriched with specific lipids, often termed lipid rafts, have been shown to modulate the physicochemical and mechanical properties of membranes and to drive protein sorting. Novel methods and tools enabling the visualization, characterization, and/or manipulation of membrane compartmentalization are crucial to link the properties of the membrane with cell functions. Flipper, a commercially available fluorescent membrane tension probe, has become a reference tool for quantitative membrane tension studies in living cells. Here, we report on a so far unidentified property of Flipper, namely, its ability to photosensitize singlet oxygen (¹O₂) under blue light when embedded into lipid membranes. This in turn results in the production of lipid hydroperoxides that increase membrane tension and trigger phase separation. In biological membranes, the photoinduced segregated domains retain the sorting ability of intact phase-separated membranes, directing raft and nonraft proteins into ordered and disordered regions, respectively, in contrast to radical-based photo-oxidation reactions that disrupt raft protein partitioning. The dual tension reporting and photosensitizing abilities of Flipper enable simultaneous visualization and manipulation of the mechanical properties and lateral organization of membranes, providing a powerful tool to optically control lipid raft formation and to explore the interplay between membrane biophysics and cell function.