Lebedev Andrey A, Vagin Alexei A, Murshudov Garib N
Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5YW, England.
Acta Crystallogr D Biol Crystallogr. 2006 Jan;62(Pt 1):83-95. doi: 10.1107/S0907444905036759. Epub 2005 Dec 14.
Entries deposited in the Protein Data Bank as of February 2004 for which both model and X-ray data were available were analysed to identify cases of twinning using such simple statistics as the R factor between potential twin-related reflections. Careful consideration of all identified twins showed that in many cases twinning was ignored during structure solution and refinement. Manual analysis of the models showed that twinning often occurs in association with rotational pseudosymmetry parallel to the twinning operator. The coexistence of these two phenomena complicates the detection and diagnostics of twinning using currently available twinning tests. It was concluded that a twinning-detection step should be incorporated in every stage of structure analysis from data acquisition to refinement and validation.
对截至2004年2月存入蛋白质数据库的条目进行分析，这些条目既有模型数据又有X射线数据，通过诸如潜在孪晶相关反射之间的R因子等简单统计数据来识别孪晶情况。对所有识别出的孪晶进行仔细考虑后发现，在许多情况下，孪晶在结构解析和精修过程中被忽略了。对模型的人工分析表明，孪晶通常与平行于孪晶操作符的旋转假对称相关联。这两种现象的共存使得使用当前可用的孪晶测试来检测和诊断孪晶变得复杂。得出的结论是，从数据采集到精修和验证的结构分析的每个阶段都应纳入孪晶检测步骤。
