X-ray data collection from macromolecular crystals.

Instruments, methods, and software for modern macromolecular crystallography is becoming so effective that molecular biologists often can solve structures from their crystals by working "without a license." In this chapter, the authors attempt to demystify some of the apparatus and techniques by providing a roadmap. Current methods for collecting X-ray diffraction data from macromolecular crystals are described. The principles of operation of the required X-ray sources, optics, goniometers, and detectors are outlined, and a typical data collection protocol is presented. Optimization of data quality is a pivotal stage in the whole crystallographic process, so much attention is given to the detailed setting up of the experiment. This is followed by a summary of the basic ideas behind the diffraction image-processing packages and their application to data reduction. Despite the increasingly "black box" nature of these computer programs, understanding how they extract the intensities, errors, and indices from the data can make subsequent structure solution and refinement much easier.