Weygand M, Wetzer B, Pum D, Sleytr U B, Cuvillier N, Kjaer K, Howes P B, Lösche M
University for Agricultural Sciences, Center for Ultrastructure Research and Ludwig-Boltzmann-Institute for Molecular Nanotechnology, A-1180 Vienna, Austria.
Biophys J. 1999 Jan;76(1 Pt 1):458-68. doi: 10.1016/S0006-3495(99)77213-9.
The coupling of bacterial surface (S)-layer proteins to lipid membranes is studied in molecular detail for proteins from Bacillus sphaericus CCM2177 and B. coagulans E38-66 recrystallized at dipalmitoylphosphatidylethanolamine (DPPE) monolayers on aqueous buffer. A comparison of the monolayer structure before and after protein recrystallization shows minimal reorganization of the lipid chains. By contrast, the lipid headgroups show major rearrangements. For the B. sphaericus CCM2177 protein underneath DPPE monolayers, x-ray reflectivity data suggest that amino acid side chains intercalate the lipid headgroups at least to the phosphate moieties, and probably further beyond. The number of electrons in the headgroup region increases by more than four per lipid. Analysis of the changes of the deduced electron density profiles in terms of a molecular interpretation shows that the phosphatidylethanolamine headgroups must reorient toward the surface normal to accommodate such changes. In terms of the protein structure (which is as yet unknown in three dimensions), the electron density profile reveals a thickness lz approximately 90 A of the recrystallized S-layer and shows water-filled cavities near its center. The protein volume fraction reaches maxima of >60% in two horizontal sections of the S-layer, close to the lipid monolayer and close to the free subphase. In between it drops to approximately 20%. Four S-layer protein monomers are located within the unit cell of a square lattice with a spacing of approximately 131 A.
在水缓冲液上的二棕榈酰磷脂酰乙醇胺（DPPE）单层中对球形芽孢杆菌CCM2177和凝结芽孢杆菌E38 - 66重结晶的蛋白质进行了细菌表面（S）层蛋白与脂质膜耦合的分子细节研究。蛋白质重结晶前后单层结构的比较表明脂质链的重组最小。相比之下，脂质头部基团显示出主要的重排。对于DPPE单层下的球形芽孢杆菌CCM2177蛋白，X射线反射率数据表明氨基酸侧链至少插入到脂质头部基团至磷酸部分，甚至可能更远。每个脂质的头部基团区域中的电子数增加超过四个。根据分子解释对推导的电子密度分布变化的分析表明，磷脂酰乙醇胺头部基团必须朝向表面法线重新定向以适应这种变化。就蛋白质结构而言（其三维结构尚不清楚），电子密度分布揭示了重结晶的S层的厚度lz约为90 Å，并在其中心附近显示出水填充的空腔。在S层的两个水平截面中，靠近脂质单层和靠近自由亚相，蛋白质体积分数达到>60％的最大值。在两者之间它下降到约20％。四个S层蛋白单体位于间距约为131 Å的方形晶格的晶胞内。
