Oxidation of Membrane Lipids Alters the Activity of the Human Serotonin 1A Receptor.

Lipid oxidation has significant effects on lipid bilayer properties; these effects can be expected to extend to interactions between the lipid bilayer and integral membrane proteins. Given that G protein-coupled receptor (GPCR) activity is known to depend on the properties of the surrounding lipid bilayer, these proteins represent an intriguing class of molecules in which the impact of lipid oxidation on protein behavior is studied. Here, we study the effects of lipid oxidation on the human serotonin 1A receptor (5-HTR). Giant unilamellar vesicles (GUVs) containing integral 5-HTR were fabricated by the hydrogel swelling method; these GUVs contained polyunsaturated 1-palmitoyl-2-linoleoyl--glycero-3-phosphocholine (PLinPC) and its oxidation product 1-palmitoyl-2-(9'-oxo-nonanoyl)--glycero-3-phosphocholine (PoxnoPC) at various ratios. 5-HTR-integrated GUVs were also fabricated from lipid mixtures that had been oxidized by extended exposure to the atmosphere. Both types of vesicles were used to evaluate 5-HTR activity using an assay to quantify GDP-GTP exchange by the coupled G protein α subunit. Results indicated that 5-HTR activity increases significantly in bilayers containing oxidized lipids. This work is an important step in understanding how hyperbaric oxidation can change plasma membrane properties and lead to physiological dysfunction.