Wukovitz S W, Yeates T O
Department of Biomathematics, University of California, Los Angeles 90095-1766, USA.
Nat Struct Biol. 1995 Dec;2(12):1062-7. doi: 10.1038/nsb1295-1062.
One of the most puzzling observations in protein crystallography is that the various space-group symmetries occur with striking non-uniformity. Molecular close-packing has been invoked to explain similar observations for crystals of small organic compounds, but does not appear to be the dominant factor for proteins. Instead, we find that the observed frequencies for both two- and three-dimensional crystals can be explained by an entropic model. Under a requirement for connectivity, the favoured space groups are simply less restrictive than others in that they allow the molecules more rigid-body degrees of freedom and can therefore be realized in a greater number of ways. This result underscores the importance of the nucleation event in crystallization and leads to specific ideas for crystallizing water-soluble and membrane proteins.
蛋白质晶体学中最令人困惑的观察结果之一是，各种空间群对称性的出现极不均匀。分子紧密堆积已被用来解释小分子有机化合物晶体的类似观察结果，但似乎不是蛋白质的主导因素。相反，我们发现二维和三维晶体的观察频率可以用熵模型来解释。在连通性要求下，有利的空间群比其他空间群限制更少，因为它们允许分子有更多的刚体自由度，因此可以通过更多方式实现。这一结果强调了成核事件在结晶过程中的重要性，并为水溶性和膜蛋白的结晶提出了具体思路。
