Automated map sharpening by maximization of detail and connectivity.
Automated map sharpening by maximization of detail and connectivity.
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DOI：
10.1107/s2059798318004655
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发表时间：
2018-06-01
期刊：
影响因子：
--
通讯作者：
Adams PD
中科院分区：
文献类型：
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作者：
Terwilliger TC;Sobolev OV;Afonine PV;Adams PD
一个优化锐化的地图的基础上，最大限度地提高了地图的细节和连通性的程序已被开发和应用到361对沉积cryo-EM地图和相关的模型。提出了一种基于细节优化和连通性优化的地图自动锐化算法。标测图中的细节反映在包含标测图体积的固定分数的等值线表面的表面积中，其中具有高细节水平的标测图具有高表面积。锐化地图的连通性反映在由相同等值线曲面定义的连通区域的数量中，其中具有高连通性的地图具有少量连通区域。通过将这两种测量结合在一个称为“调整表面积”的度量中，可以以自动化的方式评估地图质量。该度量用于选择最佳的地图锐化参数，而不参考模型或地图的其他解释。通过优化调整的表面区域的地图锐化可以针对地图整体执行，或者可以局部地执行，从而产生局部锐化的地图。为了评估各种方法的性能，使用了一种基于地图模型相关性的简单度量，该度量可以再现最佳锐化地图的视觉选择。使用B因子（原子位移因子; ADP）设置为零的模型计算贴图-模型相关性。这种基于模型的度量被用来评估地图锐化和评估地图锐化方法，并且发现调整后的表面积的优化可以是地图锐化的有效工具。
A procedure for optimizing the sharpening of a map based on maximizing the level of detail and connectivity of the map has been developed and applied to 361 pairs of deposited cryo-EM maps and associated models. An algorithm for automatic map sharpening is presented that is based on optimization of the detail and connectivity of the sharpened map. The detail in the map is reflected in the surface area of an iso-contour surface that contains a fixed fraction of the volume of the map, where a map with high level of detail has a high surface area. The connectivity of the sharpened map is reflected in the number of connected regions defined by the same iso-contour surfaces, where a map with high connectivity has a small number of connected regions. By combining these two measures in a metric termed the ‘adjusted surface area’, map quality can be evaluated in an automated fashion. This metric was used to choose optimal map-sharpening parameters without reference to a model or other interpretations of the map. Map sharpening by optimization of the adjusted surface area can be carried out for a map as a whole or it can be carried out locally, yielding a locally sharpened map. To evaluate the performance of various approaches, a simple metric based on map–model correlation that can reproduce visual choices of optimally sharpened maps was used. The map–model correlation is calculated using a model with B factors (atomic displacement factors; ADPs) set to zero. This model-based metric was used to evaluate map sharpening and to evaluate map-sharpening approaches, and it was found that optimization of the adjusted surface area can be an effective tool for map sharpening.