Hasler L, Heymann J B, Engel A, Kistler J, Walz T
Maurice E. Müller Institute for Microscopy, Biozentrum, University of Basel, Switzerland.
J Struct Biol. 1998;121(2):162-71. doi: 10.1006/jsbi.1998.3960.
The difficulty in crystallizing channel proteins in three dimensions limits the use of X-ray crystallography in solving their structures. In contrast, the amphiphilic character of integral membrane proteins promotes their integration into artificial lipid bilayers. Protein-protein interactions may lead to ordering of the proteins within the lipid bilayer into two-dimensional crystals that are amenable to structural studies by electron crystallography and atomic force microscopy. While reconstitution of membrane proteins with lipids is readily achieved, the mechanisms for crystal formation during or after reconstitution are not well understood. The nature of the detergent and lipid as well as pH and counter-ions is known to influence the crystal type and quality. Protein-protein interactions may also promote crystal stacking and aggregation of the sheet-like crystals, posing problems in data collection. Although highly promising, the number of well-studied examples is still too small to draw conclusions that would be applicable to any membrane protein of interest. Here we discuss parameters influencing the outcome of two-dimensional crystallization trials using prominent examples of channel protein crystals and highlight areas where further improvements to crystallization protocols can be made.
通道蛋白三维结晶的困难限制了X射线晶体学在解析其结构方面的应用。相比之下，整合膜蛋白的两亲性促使它们整合到人工脂质双分子层中。蛋白质-蛋白质相互作用可能导致脂质双分子层中的蛋白质排列成二维晶体，便于通过电子晶体学和原子力显微镜进行结构研究。虽然膜蛋白与脂质的重组很容易实现，但重组过程中或重组后晶体形成的机制尚不清楚。已知去污剂和脂质的性质以及pH值和抗衡离子会影响晶体类型和质量。蛋白质-蛋白质相互作用也可能促进片状晶体的晶体堆积和聚集，给数据收集带来问题。尽管前景广阔，但经过充分研究的例子数量仍然太少，无法得出适用于任何感兴趣的膜蛋白的结论。在这里，我们以通道蛋白晶体的突出例子讨论影响二维结晶试验结果的参数，并强调可以进一步改进结晶方案的领域。
