Essen L, Siegert R, Lehmann W D, Oesterhelt D
Max-Planck-Institut fur Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Germany.
Proc Natl Acad Sci U S A. 1998 Sep 29;95(20):11673-8. doi: 10.1073/pnas.95.20.11673.
Heterogenous nucleation on small molecule crystals causes a monoclinic crystal form of bacteriorhodopsin (BR) in which trimers of this membrane protein pack differently than in native purple membranes. Analysis of single crystals by nano-electrospray ionization-mass spectrometry demonstrated a preservation of the purple membrane lipid composition in these BR crystals. The 2.9-A x-ray structure shows a lipid-mediated stabilization of BR trimers where the glycolipid S-TGA-1 binds into the central compartment of BR trimers. The BR trimer/lipid complex provides an example of local membrane thinning as the lipid head-group boundary of the central lipid patch is shifted by 5 A toward the membrane center. Nonbiased electron density maps reveal structural differences to previously reported BR structures, especially for the cytosolic EF loop and the proton exit pathway. The terminal proton release complex now comprises an E194-E204 dyad as a diffuse proton buffer.
小分子晶体上的异质成核导致细菌视紫红质（BR）形成单斜晶型，其中这种膜蛋白的三聚体堆积方式与天然紫膜中的不同。通过纳米电喷雾电离质谱对单晶进行分析表明，这些BR晶体中紫膜脂质组成得以保留。2.9埃的X射线结构显示，糖脂S-TGA-1结合到BR三聚体的中央隔室中，脂质介导了BR三聚体的稳定。BR三聚体/脂质复合物提供了局部膜变薄的一个例子，因为中央脂质斑块的脂质头基团边界向膜中心移动了5埃。无偏电子密度图揭示了与先前报道的BR结构的结构差异，特别是对于胞质EF环和质子出口途径。末端质子释放复合物现在包含一个E194-E204二元组作为扩散质子缓冲剂。
