Giant Phospholipid Folds on Air-Water Surface: Structure Details, Formation Pathway, and Possible Recycle Mechanism

In vitro mimics recognized that the propensity of a negatively charged phospholipid, DPPS, monolayers to self-aggregate to three-dimensional (3D) giant folds under overcompression at an air-water interface. Time elapsing microscopical observations confirmed that such giant folds were able to float stably on the air-water interface for weeks or even longer. Ex situ atomic force microscopy (AFM) and transmission electronic microscopy (TEM) characterizations pointed out that such giant folds were composed of compactly stacked lipid layers. Phospholipase A₂ (PLA₂), a principal bactericide in human and animal tear secretion, was chosen to drive the in situ lipid giant folds disassembly on water and supported substrate surfaces, respectively. Our experimental results confirmed the layer-by-layer structures of the giant folds. It is noteworthy that the defect-rich areas of the giant lipid folds were eliminated quickly by PLA₂ while defect-free lipid zones were left untouched, suggesting that PLA₂ may serve as a highly effective and selective regenerator/cleaner of lipid aggregates in the physiological circumstance of certain organs.