Schuster B, Sleytr U B
Center for Ultrastructure Research and Ludwig Boltzmann Institute for Molecular Nano-technology, Universität für Bodenkultur Wien, Gregor-Mendel-Strasse 33, A-1180 Vienna, Austria.
J Biotechnol. 2000 Sep;74(3):233-54. doi: 10.1016/s1389-0352(00)00014-3.
Many prokaryotic organisms (archaea and bacteria) are covered by a regularly ordered surface layer (S-layer) as the outermost cell wall component. S-layers are built up of a single protein or glycoprotein species and represent the simplest biological membrane developed during evolution. Pores in S-layers are of regular size and morphology, and functional groups on the protein lattice are aligned in well-defined positions and orientations. Due to the high degree of structural regularity S-layers represent unique systems for studying the structure, morphogenesis, and function of layered supramolecular assemblies. Isolated S-layer subunits of numerous organisms are able to assemble into monomolecular arrays either in suspension, at air/water interfaces, on planar mono- and bilayer lipid films, on liposomes and on solid supports (e.g. silicon wafers). Detailed studies on composite S-layer/lipid structures have been performed with Langmuir films, freestanding bilayer lipid membranes, solid supported lipid membranes, and liposomes. Lipid molecules in planar films and liposomes interact via their head groups with defined domains on the S-layer lattice. Electrostatic interactions are the most prevalent forces. The hydrophobic chains of the lipid monolayers are almost unaffected by the attachment of the S-layer and no impact on the hydrophobic thickness of the membranes has been observed. Upon crystallization of a coherent S-layer lattice on planar and vesicular lipid membranes, an increase in molecular order is observed, which is reflected in a decrease of the membrane tension and an enhanced mobility of probe molecules within an S-layer-supported bilayer. Thus, the terminology 'semifluid membrane' has been introduced for describing S-layer-supported lipid membranes. The most important feature of composite S-layer/lipid membranes is an enhanced stability in comparison to unsupported membranes.
许多原核生物（古细菌和细菌）的最外层细胞壁成分是一层规则排列的表面层（S层）。S层由单一蛋白质或糖蛋白构成，是进化过程中形成的最简单的生物膜。S层中的孔具有规则的大小和形态，蛋白质晶格上的官能团在明确的位置和取向上排列。由于高度的结构规则性，S层是研究层状超分子组装体的结构、形态发生和功能的独特系统。许多生物体分离出的S层亚基能够在悬浮液中、空气/水界面、平面单分子和双分子脂质膜上、脂质体上以及固体支持物（如硅片）上组装成单分子阵列。已经使用朗缪尔膜、独立双层脂质膜、固体支持脂质膜和脂质体对复合S层/脂质结构进行了详细研究。平面膜和脂质体中的脂质分子通过其头部基团与S层晶格上的特定区域相互作用。静电相互作用是最普遍的作用力。脂质单层的疏水链几乎不受S层附着的影响，并且未观察到对膜疏水厚度的影响。当在平面和囊泡脂质膜上形成连贯的S层晶格时，观察到分子有序性增加，这反映在膜张力降低以及S层支持的双层内探针分子的流动性增强。因此，引入了“半流体膜”这一术语来描述S层支持的脂质膜。与无支撑的膜相比，复合S层/脂质膜的最重要特征是稳定性增强。
