Section: Application Domains
X-ray structure analysis is the main tool to establish the three-dimensional atomic structure of biological macromolecules and their complexes. The determination of a structure in X-ray crystallography passes through several stages:
purification and crystallization of the object under study (a protein, DNA, RNA, virus, or a huge macromolecular complex, such as ribosome or lipoprotein particles);
X-ray experiment (usually at synchrotron accelerators); data collection (up to a million of independent observations) and their primary processing;
the solution of the inverse problem of the theory of diffraction to find the electron density distribution in the studied object and to interpret it in terms of atoms.
A key problem of X-ray structure analysis is the so-called phase problem . In an X-ray experiment, one can measure only the magnitudes of the complex Fourier coefficients of the electron density distribution under study, but not their phases. Half of the necessary information is therefore lost, and must be restored by other means.