Welberry T R, Heerdegen A P, Goldstone D C, Taylor Ian A
Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
Acta Crystallogr B. 2011 Dec;67(Pt 6):516-24. doi: 10.1107/S0108768111037542. Epub 2011 Oct 13.
Distinctive diffuse scattering in the form of diffuse rings around Bragg positions has been observed in the diffraction patterns of a crystal of the N-terminal fragment of the Gag protein from Feline Foamy Virus. It is shown that these are caused by geometric frustration as molecules try to pack on the triangular b-c mesh of the space group P6(1)22. In order to explain the strong diffuse scattering it is necessary for the crystal to contain occupational disorder such that each unit cell contains one or other of two different molecular arrangements, A and B. The frustration arises because the nearest-neighbour packing prefers neighbouring cells to be AB or BA, which cannot be achieved on all three sides of a triangle simultaneously. To explain the observation that reciprocal sections hk5n, where n = integer, contain only Bragg peaks it is necessary that A and B are identical molecular arrangements differing only by a translation of 0.2c. The implications of the disorder for solving the structure of the protein by conventional techniques as well as the possibility of using the diffuse scattering for this purpose are discussed.
在猫泡沫病毒Gag蛋白N端片段晶体的衍射图谱中，观察到了以布拉格位置周围的漫射环形式存在的独特漫散射。结果表明，这些是由于分子试图堆积在空间群P6(1)22的三角形b - c网格上时的几何受挫所致。为了解释强烈的漫散射，晶体必须包含占位无序，使得每个晶胞包含两种不同分子排列A和B中的一种。受挫的原因是最近邻堆积倾向于相邻晶胞为AB或BA，但在三角形的所有三条边上不能同时实现。为了解释倒易截面hk5n（其中n为整数）仅包含布拉格峰这一观察结果，A和B必须是仅相差0.2c平移的相同分子排列。讨论了这种无序对通过传统技术解析蛋白质结构的影响以及利用漫散射实现这一目的的可能性。
