Joint Studies on Functional Role of Archaeal Macrocyclic Lipids

古细菌包括产甲烷菌、极端嗜盐菌、极端嗜热菌和热嗜酸菌，它们在相当特殊的条件下生长，具有结构独特的膜脂以适应极端环境。脂质由疏水类异戊二烯链组成，通过醚键与甘油相连，这与真核和真细菌膜脂的酯键形成鲜明对比。古菌醚脂质最显著的特征是其大环（36元或72元）结构。这些不寻常的脂质与基于脂质双层结构的物理化学性质有关。我们对这些脂质的兴趣集中在大环分子结构的生化意义上。采用差示扫描量热法、电子显微镜和光学显微镜、停止流动/光散射和固态^2H-NMR技术研究了合成的36元古菌磷脂的一些生物物理性质。这种磷脂在水中具有多种自组织结构，特别是囊泡和小管。观察到这种古菌磷脂的一些特殊膜性质：它们在很宽的温度范围内呈液晶状态；其聚戊烯基链的动力学高于n-酰基链；膜的透水性低于n-酰基磷脂膜。研究还发现，大环化显著提高了膜的水屏障性能和膜的稳定性。这可能与jannaschi甲烷球菌对深海热液喷口极端环境的适应有关。此外，通过相对比和荧光观察了合成的72元大环四醚磷酸盐（Sulfolobus, Thermoplasma, methanogenic Archaea）的主要磷脂组分)的自组装性质。72元大环偶极磷酸盐自发形成囊泡。少

Archaea including methanogens, extreme halophiles, extreme thermophiles and thermoacidophiles grow under rather extraordinary conditions and have structurally unique membrane lipids to adapt the extreme environments. The lipids are consisted of hydrophobic isoprenoid chains linked to glycerol with the ether bonds, which are well contrast to the ester linkage of the eubacterial and eukaryotic membrane lipids. The most striking feature of the archaeal ether lipid is found in the macrocyclic (36-or72-membered) ring structures. These unusual lipids have been interested in connection with the physicochemical properties based on the lipid bilayer structure. Our interest in these lipids focuses on the biochemical significance of the macrocyclic molecular structures.Some biophysical properties of synthetic 36-membered archaeal phospholipids were studied using differential scanning calorimetry, electron and optical microscopies, stopped-flow/light scattering and solid-state ^2H-NMR techniques. … More This phospholipid gave a variety of self-organized structures in water, in particular vesucles and tubules. Some specific membrane properties of this archaeal phospholipid were observed : they are in a liquid-crystalline state over a wide temperature range ; the dynamics of their polyprenyl chains is higher than that of n-acyl chains ; the water permeability of the membranes is lower than that of n-acyl phosholipid membranes. It was also found that macrocyclization improves remarkably the barrier proprtlies to water and the membrane stability. This may be related to the adaptation of Methanococcus jannaschii to the extreme conditions of the deep-sea hydrothermal vents.Further, the self-assembly properties of 72-membered macrocyclic tetraether phosphates, the major phospholipid components of Sulfolobus, Thermoplasma and methanogenic Archaea, which were also synthesized, were observed by phase contrast and fluorescence. The 72-membered macrocyclic dipolar phosphates formed spontaneously vesicles. Less