阐述蛋白质、DNA或其它生物分子的原子水平的三维结构的技术。这种方法的运用是基于首先使纯化的生物分子结晶为有序排列然后用X射线分析结晶体。之所以使用X射线是因为其波长和原子裂解时的波长一样，所以晶体作为分子衍射光栅衍射X射线，产生一种可以获取并分析的衍射图形。然后用计算机重建初始结构。在实际操作中这一衍射图形被反复地不断升高的分辨率处理，结晶学家不断在建立一个模型结构并按该模型计算出的衍射图形与实际观察到的比较。每一次重复都使模型结构与实验结果更加吻合。当这两者之间的差异可以忽略时，这一衍射图形便得到求解。最终的模型提供了被研究分子平均时间上的三维原子水平结构。蛋白靶子的X射线结晶体结构可以识别蛋白质的功能袋。当与自然或人工配体混合时，可以作为药物设计的有用起始点。蛋白质X射线结构的目录也为蛋白质结构类型、自然状态下的折叠和域提供了有用信息。有时这被称为结构基因组学。

A technique that allows the elucidation of the three-dimensional structure of proteins, DNA, or other biomolecules at atomic-level resolution. This is achieved by first crystallizing the purified biomolecule into ordered arrays and then using X-ray diffraction to analyze the crystals. X-rays are used because they have the same wavelength as the atomic separations so the crystal acts as a molecular diffraction grating to diffract a beam of X-rays, producing a diffraction pattern that can be captured and analyzed. A computer is then used to reconstruct the original structure. In practice the diffraction pattern is iteratively solved at ever-increasing “shells” of resolution; the crystallographer alternates between building a model structure (working in “real” space) and comparing the model’s calculated diffraction pattern with the observed diffraction pattern (working in “reciprocal” space). Each round of iteration brings the model structure into better agreement with the experimental data; when the difference between the two is negligible the diffraction pattern is said to be “solved.” The final model provides a time-averaged three-dimensional atomic-resolution structure of the molecule under study. The X-ray crystal structure of a protein target can identify the functional pockets of the protein and, when complexed with a natural or synthetic ligand, can serve as a useful starting point for rational drug design. X-ray structures of catalogs of proteins have also provided useful information on the types of protein structures, folds and domains found in nature; this is sometimes termed structural genomics.