Group of Biophysics, Department of Physics, Faculty of Science, University of Ostrava, 710 00 Ostrava, Czech Republic.
Slovenian NMR Center, National Institute of Chemistry, SI-1000 Ljubljana, Slovenia.
Cells. 2021 Sep 8;10(9):2354. doi: 10.3390/cells10092354.
Build-up of the energized state of thylakoid membranes and the synthesis of ATP are warranted by organizing their bulk lipids into a bilayer. However, the major lipid species of these membranes, monogalactosyldiacylglycerol, is a non-bilayer lipid. It has also been documented that fully functional thylakoid membranes, in addition to the bilayer, contain an inverted hexagonal (H) phase and two isotropic phases. To shed light on the origin of these non-lamellar phases, we performed P-NMR spectroscopy experiments on sub-chloroplast particles of spinach: stacked, granum and unstacked, stroma thylakoid membranes. These membranes exhibited similar lipid polymorphism as the whole thylakoids. Saturation transfer experiments, applying saturating pulses at characteristic frequencies at 5 °C, provided evidence for distinct lipid phases-with component spectra very similar to those derived from mathematical deconvolution of the P-NMR spectra. Wheat-germ lipase treatment of samples selectively eliminated the phases exhibiting sharp isotropic peaks, suggesting easier accessibility of these lipids compared to the bilayer and the H phases. Gradually increasing lipid exchanges were observed between the bilayer and the two isotropic phases upon gradually elevating the temperature from 5 to 35 °C, suggesting close connections between these lipid phases. Data concerning the identity and structural and functional roles of different lipid phases will be presented in the accompanying paper.
类囊体膜的激发态的建立和 ATP 的合成需要通过将其大量脂质组织成双层来保证。然而，这些膜的主要脂质种类，即单半乳糖二酰基甘油，是一种非双层脂质。此外，有文献记载，除了双层之外，功能齐全的类囊体膜还包含一个反六角形（H）相和两个各向同性相。为了阐明这些非层状相的起源，我们对菠菜亚叶绿体颗粒进行了 P-NMR 光谱实验：堆叠的、粒状的和未堆叠的基质类囊体膜。这些膜表现出与整个类囊体相似的脂质多态性。饱和转移实验在 5°C 下在特征频率处施加饱和脉冲，为不同的脂质相提供了证据-其组成谱与从 P-NMR 谱的数学反卷积得出的谱非常相似。用小麦胚芽脂肪酶处理样品选择性地消除了具有尖锐各向同性峰的相，表明与双层和 H 相相比，这些脂质更容易接近。逐渐升高温度从 5 到 35°C 时，观察到双层和两个各向同性相之间的脂质交换逐渐增加，这表明这些脂质相之间存在密切联系。关于不同脂质相的身份、结构和功能作用的数据将在随附的论文中呈现。
