Hattne Johan, Lamzin Victor S
European Molecular Biology Laboratory, c/o DESY, Notkestrasse 85, 22603 Hamburg, Germany.
Acta Crystallogr D Biol Crystallogr. 2008 Aug;D64(Pt 8):834-42. doi: 10.1107/S0907444908014327. Epub 2008 Jul 17.
A pattern-recognition-based method for the detection of planar objects in protein or DNA/RNA crystal structure determination is described. The procedure derives a set of rotation-invariant numeric features from local regions in the asymmetric unit of a crystallographic electron-density map. These features, primarily moments of various orders, capture different aspects of the local shape of objects in the electron density. Feature classification is achieved using a linear discriminant that is trained to optimize the contrast between planar and nonplanar objects. In five selected test cases with X-ray data spanning 2.0-3.0 A resolution, the procedure identified the correct location and orientation for almost all of the double-ring and a majority of the single-ring planar groups. The accuracy of the location of the plane centres is of the order of 0.5 A, even in moderately noisy density maps.
本文描述了一种基于模式识别的方法，用于在蛋白质或DNA/RNA晶体结构测定中检测平面物体。该过程从晶体学电子密度图的不对称单元中的局部区域导出一组旋转不变的数字特征。这些特征主要是不同阶次的矩，捕捉了电子密度中物体局部形状的不同方面。使用线性判别式进行特征分类，该判别式经过训练以优化平面物体和非平面物体之间的对比度。在五个选定的测试案例中，使用分辨率在2.0 - 3.0埃的X射线数据，该过程几乎为所有双环和大多数单环平面基团确定了正确的位置和方向。即使在噪声适中的密度图中，平面中心位置的准确性也约为0.5埃。
