Glycolipids slow interfacial proton migration while preserving surface proton retention

Area of Science:

• Biochemistry
• Membrane Biophysics
• Physical Chemistry

Background:

• Proton gradients are crucial for biological energy transduction.
• Regulation of interfacial proton migration at membranes is poorly understood.
• Understanding proton transport is key to diverse cellular processes.

Purpose of the Study:

• To quantify the impact of membrane composition on interfacial proton migration.
• To elucidate the role of membrane charge versus lipid composition in proton diffusion.
• To establish a mechanistic framework for proton coupling in biological membranes.

Main Methods:

• Utilized an approach releasing protons at membrane surfaces via embedded ionophores.
• Employed fluorometry to monitor proton arrival across membrane patches.
• Investigated proton migration across neutral, negatively, and positively charged membranes, as well as those with incorporated glycolipids.

Main Results:

• Membrane charge had modest effects on lateral proton diffusion and surface-to-bulk release barriers.
• Incorporation of thylakoid membrane glycolipids (digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol) significantly reduced lateral proton diffusion.
• Glycolipids had minimal impact on the surface-to-bulk proton release barrier.

Conclusions:

• Interfacial proton migration is primarily governed by hydration-layer properties, not membrane electrostatics.
• Membrane-anchored sugars act as potent regulators of long-range proton conduction.
• These findings provide insights into localized proton coupling in glycolipid-rich biological membranes.