Glycolipids slow interfacial proton migration while preserving surface proton retention

Proton gradients power diverse biological processes, yet how interfacial proton migrationis regulated remains unclear. Here we quantify how membrane composition controlsinterfacial proton migration using an approach that releases protons directly at thesurface of a membrane patch via an embedded ionophore. Fluorometrically monitoringproton arrival at a distant patch across neutral, negatively charged, and positivelycharged membranes, we confirm that both the lateral surface diffusion coefficient andthe activation barrier for proton release into the bulk vary rather modestly. In contrastto membrane electrostatics, membrane incorporation of glycolipids typical of thylakoidmembranes—digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol—leads to amore pronounced reduction of the lateral proton diffusion coefficient, with comparativelysmall effects on the surface-to-bulk release barrier. Thus, interfacial proton migrationis governed primarily by hydration-layer properties rather than membrane charge.These results establish membrane-anchored sugars as potent modulators of long-rangeproton conduction and provide a mechanistic framework for localized proton couplingin glycolipid-rich biological membranes.