Raft Affinity and Membrane Modulation of Docosahexaenoic Acid-Containing Phospholipids Revealed by Comparative...

Docosahexaenoic acid (DHA, C22:6) is a polyunsaturated fatty acid that is abundant in the brain. It is also present in biological membranes as DHA-containing phospholipids (DHA-PLs). DHA-PLs are known to modulate lipid rafts; however, the underlying molecular mechanism has not been fully elucidated, primarily owing to the lack of methods to analyze the behavior of DHA-PLs in membranes at the molecular level. To address this, we synthesized a fluorescently labeled DHA-PL using our previously developed labeling method that preserves the intrinsic physicochemical behavior of lipids. For comparison, a fluorescent analog of arachidonic acid-containing phospholipids (AA-PLs) was also prepared. Using these fluorescently labeled lipids, we measured their lateral diffusion coefficients and partitioning ratios in phase-separated membranes. The results demonstrate that DHA-PL exhibits a higher affinity for lipid raft-like domains than AA-PL and that its incorporation induces compositional changes and modulates raft-like membrane organization. This study clearly demonstrates how subtle differences in unsaturated acyl chains affect phospholipid behavior in membranes and establishes our labeling technology as a powerful platform for probing the molecular behavior of polyunsaturated phospholipids in membranes.