Abstract：
Enzyme-mediated lipid oxidation is an important regulatory event in cell signaling, with oxidized lipids being potent signaling molecules that can illicit dramatic changes in cell behavior. For example, peroxidation of an arachidonoyl poly-unsaturated fatty acid by the human enzyme 15-lipoxygenase-2 (15-LOX-2) has been associated with formation of atherosclerotic plaques. Previous work on synthetically oxidized membranes has shown that oxidized lipid tails will change their conformation to facilitate interactions between the peroxide group and the lipid headgroups. However, this phenomenon has not been directly observed for a lipid membrane that has undergone enzyme-catalyzed oxidation. In this study, we report on the structure of a model lipid membrane before and after oxidation by 15-LOX-2. A model lipid membrane monolayer at the air-liquid interface was constructed from 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (SAPC) in a Langmuir trough, and X-ray reflectivity measurements were conducted to determine the electron density profile of the system. Exposure to 15-LOX-2 caused a dramatic change in the SAPC structure, namely a blurred distinction between the lipid tail/head layers and shortening of the average lipid tail length by ∼3 Å. The electron density profile of the oxidized SAPC monolayer is similar to that of a synthetically oxidized substrate mimic. Overall, this reported observation of an enzymatically-oxidized membrane structure in situ is helping to bridge a gap in the literature between structural studies on synthetically oxidized membranes and cellular studies aiming to understand physiological responses.
摘要：
酶介导的脂质氧化是细胞信号传导的重要调控事件,氧化脂质是有效的信号分子，可以破坏细胞行为的戏剧性变化。例如,人酶15-脂氧合酶-2（15-LOX-2）对花生四酰基多不饱和脂肪酸的过氧化与动脉粥样硬化斑块的形成有关。先前对合成氧化膜的工作表明，氧化的脂质尾巴会改变其构象，以促进过氧化物基团和脂质头基之间的相互作用。然而,对于经历了酶催化氧化的脂质膜，这种现象尚未直接观察到。在这项研究中,我们报告了15-LOX-2氧化前后模型脂质膜的结构。由Langmuir槽中的1-硬脂酰-2-花生四酰基-sn-甘油-3-磷酸胆碱（SAPC）构建了气液界面处的模型脂质膜单层，进行X射线反射率测量以确定系统的电子密度分布。暴露于15-LOX-2引起SAPC结构的戏剧性变化，即脂质尾部/头部层之间的模糊区别和平均脂质尾部长度的缩短〜3。氧化的SAPC单层的电子密度分布类似于合成氧化的底物模拟物的电子密度分布。总的来说,据报道，对酶促氧化膜结构的原位观察有助于弥合文献中合成氧化膜结构研究与旨在了解生理反应的细胞研究之间的空白。
