Landau E M, Rosenbusch J P
Biozentrum, University of Basel, Switzerland.
Proc Natl Acad Sci U S A. 1996 Dec 10;93(25):14532-5. doi: 10.1073/pnas.93.25.14532.
Understanding the mechanisms of action of membrane proteins requires the elucidation of their structures to high resolution. The critical step in accomplishing this by x-ray crystallography is the routine availability of well-ordered three-dimensional crystals. We have devised a novel, rational approach to meet this goal using quasisolid lipidic cubic phases. This membrane system, consisting of lipid, water, and protein in appropriate proportions, forms a structured, transparent, and complex three-dimensional lipidic array, which is pervaded by an intercommunicating aqueous channel system. Such matrices provide nucleation sites ("seeding") and support growth by lateral diffusion of protein molecules in the membrane ("feeding"). Bacteriorhodopsin crystals were obtained from bicontinuous cubic phases, but not from micellar systems, implying a critical role of the continuity of the diffusion space (the bilayer) on crystal growth. Hexagonal bacteriorhodopsin crystals diffracted to 3.7 A resolution, with a space group P6(3), and unit cell dimensions of a = b = 62 A, c = 108 A; alpha = beta = 90 degrees and gamma = 120 degrees.
要理解膜蛋白的作用机制，需要将其结构解析到高分辨率。通过X射线晶体学实现这一目标的关键步骤是常规获得有序的三维晶体。我们设计了一种新颖、合理的方法，利用准固态脂质立方相来实现这一目标。这种膜系统由适当比例的脂质、水和蛋白质组成，形成一种结构化、透明且复杂的三维脂质阵列，其中充满了相互连通的水通道系统。这样的基质提供成核位点（“播种”），并通过蛋白质分子在膜中的横向扩散（“供给”）来支持晶体生长。细菌视紫红质晶体是从双连续立方相中获得的，而不是从胶束系统中获得的，这意味着扩散空间（双层膜）的连续性对晶体生长起着关键作用。六方细菌视紫红质晶体的衍射分辨率达到3.7 Å，空间群为P6(3)，晶胞参数为a = b = 62 Å，c = 108 Å；α = β = 90°，γ = 120°。
