Deciphering Melatonin-Stabilized Phase Separation\nin Phospholipid Bilayers

Abstract

Lipid\nbilayers are fundamental building blocks of cell membranes, which\ncontain the machinery needed to perform a range of biological functions,\nincluding cell–cell recognition, signal transduction, receptor\ntrafficking, viral budding, and cell fusion. Importantly, many of\nthese functions are thought to take place in the laterally phase-separated\nregions of the membrane, commonly known as lipid rafts. Here, we provide\nexperimental evidence for the “stabilizing” effect of\nmelatonin, a naturally occurring hormone produced by the brain’s\npineal gland, on phase-separated model membranes mimicking the outer\nleaflet of plasma membranes. Specifically, we show that melatonin\nstabilizes the liquid-ordered/liquid-disordered phase coexistence\nover an extended range of temperatures. The melatonin-mediated stabilization\neffect is observed in both nanometer- and micrometer-sized liposomes\nusing small angle neutron scattering (SANS), confocal fluorescence\nmicroscopy, and differential scanning calorimetry. To experimentally\ndetect nanoscopic domains in 50 nm diameter phospholipid vesicles,\nwe developed a model using the Landau–Brazovskii approach that\nmay serve as a platform for detecting the existence of nanoscopic\nlateral heterogeneities in soft matter and biological materials with\nspherical and planar geometries.