Effect of oxidation of polyunsaturated phospholipids on the binding of proteins in monolayers.

Polyunsaturated fatty acids (PUFA) are particularly susceptible to oxidation. The resulting oxidized products may exert toxic effects. In particular, information is lacking on the effect of oxidized polyunsaturated phospholipid membranes on protein binding. This is particularly important for photoreceptors where many processes take place at the membrane surface because of their very large content in polyunsaturated phospholipids. Langmuir monolayers were thus used to determine the effect of oxidized phospholipids on the binding parameters of two proteins located in photoreceptors: Retinitis pigmentosa 2 (RP2) and recoverin. Measurements were performed using lipid oxidized during storage in solution and directly at the air-water interface. Large differences were observed between the binding parameters of RP2 and recoverin in the presence of intact and oxidized 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine (DDPC). Indeed, large decreases of the maximum insertion pressure, ΔΠ0 and ΔΠ were observed when protein binding was compared between intact and oxidized DDPC. Altered protein binding in the presence of oxidized lipids could thus lead to improper membrane processes and various cellular malfunctioning and diseases.