PDF(Pubmed)
Abstract：
One of the great challenges in refining macromolecular crystal structures is a low data-to-parameter ratio. Historically, knowledge from chemistry has been used to help to improve this ratio. When a macromolecule crystallizes with more than one copy in the asymmetric unit, the noncrystallographic symmetry relationships can be exploited to provide additional restraints when refining the working model. However, although globally similar, NCS-related chains often have local differences. To allow for local differences between NCS-related molecules, flexible torsion-based NCS restraints have been introduced, coupled with intelligent rotamer handling for protein chains, and are available in phenix.refine for refinement of models at all resolutions.
摘要：
精炼大分子晶体结构的最大挑战之一是低数据参数比。历史上,来自化学的知识已被用来帮助提高这一比率。当大分子在不对称单元中结晶不止一个拷贝时，在完善工作模型时，可以利用非晶体学对称关系来提供额外的限制。然而,虽然全球相似，与NCS相关的链通常具有局部差异。为了允许NCS相关分子之间的局部差异，引入了基于柔性扭转的NCS约束，再加上蛋白质链的智能旋转异构体处理，并在phenix中可用。在所有分辨率下细化模型。
