Augustynska Dominika, Jemioła-Rzemińska Małgorzata, Burda Kvetoslava, Strzałka Kazimierz
AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Mickiewicza 30, 30-059 Kraków, Poland.
Jagiellonian University, Faculty of Biochemistry, Biophysics and Biotechnology, Gronostajowa 7, 30-387 Kraków, Poland; Małopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
Chem Biol Interact. 2015 Sep 5;239:19-25. doi: 10.1016/j.cbi.2015.06.021. Epub 2015 Jun 20.
Carotenoids, which are known primarily for their photoprotective and antioxidant properties, may also strongly influence the physical properties of membranes. The localization and orientation of these pigments in the lipid bilayer depends on their structure and is determined by their interactions with lipid molecules. This affects both phase behavior and the mechanical properties of membranes. Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) allowed us to gain a direct insight into the differences between the interaction of the non-polar β-carotene and polar zeaxanthin embedded into DPPC liposomes. DSC results showed that zeaxanthin, having polar ionone rings, interacts more strongly with the membrane lipids than β-carotene. The decrease in molar heat capacity by a factor of 2 with a simultaneous broadening of the main phase transition (gel-to-liquid crystalline phase transition) as compared to the two other systems studied suggests some increased length of the coupled interactions between the polar xanthophyll and lipids. Long-distance interactions lead to the formation of larger clusters which may exhibit higher flexibility than small clusters when only short-distance interactions occur. AFM experiments show that adhesive forces are 2 and 10 times higher for DPPC membranes enriched in β-carotene and zeaxanthin, respectively, than those observed for an untreated system. Temperature dependent measurements of adhesion revealed that subphases can be formed in the gel lamellar state of DPPC bilayers. The presence of the non-polar carotenoid enhanced the effect and even a bifurcation of the substates was detected within a temperature range of 30.0-32.5°C prior to pretransition. It is the first time when the presence of subphases has been demonstrated. This knowledge can be helpful in better understanding the functioning of carotenoids in biological membranes. AFM seem to be a very unique and sensitive method for detecting such fine changes in the lipid bilayers.
类胡萝卜素主要因其光保护和抗氧化特性而闻名，它们也可能对膜的物理性质产生强烈影响。这些色素在脂质双层中的定位和取向取决于它们的结构，并由它们与脂质分子的相互作用决定。这会影响膜的相行为和机械性能。差示扫描量热法（DSC）和原子力显微镜（AFM）使我们能够直接洞察嵌入二棕榈酰磷脂酰胆碱（DPPC）脂质体中的非极性β-胡萝卜素和极性玉米黄质相互作用的差异。DSC结果表明，具有极性紫罗酮环的玉米黄质与膜脂质的相互作用比β-胡萝卜素更强。与其他两个研究系统相比，摩尔热容降低了2倍，同时主相变（凝胶-液晶相变）变宽，这表明极性叶黄素与脂质之间的耦合相互作用长度有所增加。长距离相互作用导致形成更大的簇，当只发生短距离相互作用时，这些簇可能比小簇表现出更高的柔韧性。AFM实验表明，富含β-胡萝卜素和玉米黄质的DPPC膜的粘附力分别比未处理系统高2倍和10倍。对粘附力的温度依赖性测量表明，在DPPC双层的凝胶层状状态下可以形成亚相。非极性类胡萝卜素的存在增强了这种效应，甚至在预转变前30.0-32.5°C的温度范围内检测到亚状态的分叉。这是首次证明亚相的存在。这一知识有助于更好地理解类胡萝卜素在生物膜中的功能。AFM似乎是检测脂质双层中这种细微变化的一种非常独特和灵敏的方法。
