Cardoso Renato M S, Lairion Fabiana, Disalvo Edgardo Anibal, Loura Luís M S, Moreno Maria João
Coimbra Chemistry Center, Institute of Molecular Sciences (CQC-IMS), University of Coimbra, 3004-535 Coimbra, Portugal.
Chemistry Department, Faculty of Science and Technology, University of Coimbra, 3004-535 Coimbra, Portugal.
Molecules. 2024 Dec 11;29(24):5843. doi: 10.3390/molecules29245843.
The membrane dipole potential that arises from the interfacial water and constitutive dipolar groups of lipid molecules modulates the interaction of amphiphiles and proteins with membranes. Consequently, its determination for lipid mixtures resembling the existing diversity in biological membranes is very relevant. In this work, the dipole potentials of monolayers, formed at the air-water interface, from pure or mixed lipids (1-palmitoyl-2-oleoyl--glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl--glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2-oleoyl--glycero-3-phosphatidyserine (POPS), sphingomyelin (SpM) and cholesterol) were measured and correlated with the mean area per lipid. The results showed that, as previously observed, cholesterol increases the dipole potential in correspondence with the decrease in the average area per lipid. At the small mole fractions encountered in biomembranes, the presence of the negatively charged lipid POPS increases the dipole potentials of monolayers despite inducing an increase in the average area per lipid. Additionally, the inclusion of POPE in POPC:cholesterol monolayers disrupts the area condensation induced by cholesterol while increasing the membrane dipole moment, leading to a small reduction in the dipole potential. This trend is reinforced for the quaternary POPC:cholesterol:POPE:POPS 4:3:2:1 system, which mimics the inner leaflets of eukaryotic plasma membranes. In agreement with previous works, the replacement of phosphocholine lipids with sphingomyelin leads to a decrease in the dipole potential. Together, this results in a lower dipole potential for the SpM-enriched outer leaflet, generating a non-zero transbilayer dipole potential in the asymmetric plasma membranes of eukaryotic cells.
由界面水和脂质分子的组成性偶极基团产生的膜偶极电位调节两亲分子和蛋白质与膜的相互作用。因此，测定类似于生物膜中现有多样性的脂质混合物的偶极电位非常重要。在这项工作中，测量了在空气-水界面形成的纯脂质或混合脂质（1-棕榈酰-2-油酰基-sn-甘油-3-磷酸胆碱（POPC）、1-棕榈酰-2-油酰基-sn-甘油-3-磷酸乙醇胺（POPE）、1-棕榈酰-2-油酰基-sn-甘油-3-磷脂酰丝氨酸（POPS）、鞘磷脂（SpM）和胆固醇）单分子层的偶极电位，并将其与每个脂质的平均面积相关联。结果表明，如先前观察到的，胆固醇增加偶极电位，同时每个脂质的平均面积减小。在生物膜中遇到的小摩尔分数下，带负电荷的脂质POPS的存在增加了单分子层的偶极电位，尽管它导致每个脂质的平均面积增加。此外，在POPC:胆固醇单分子层中加入POPE会破坏胆固醇诱导的面积凝聚，同时增加膜偶极矩，导致偶极电位略有降低。对于模拟真核细胞质膜内小叶的季铵盐POPC:胆固醇:POPE:POPS 4:3:2:1系统，这种趋势得到加强。与先前的研究一致，用鞘磷脂取代磷酸胆碱脂质会导致偶极电位降低。总之，这导致富含SpM的外小叶的偶极电位较低，在真核细胞的不对称质膜中产生非零的跨膜偶极电位。
