16 Principles and Practice in Macromolecular X‐Ray Crystallography
Arnaud Baslé and Richard J. Lewis
Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
16.1 Significance and Short Background
To understand the function of proteins we need to observe them on the atomic scale in 3D. Proteins can be as small as 5 nm and even large complexes, like ribosomes, are only 30 nm in diameter. The length of covalent bonds in proteins, ∼0.15 nm, is simply too short to be observed using the visible portion, 400–700 nm, of the electromagnetic spectrum. A form of illumination has to be used that is better matched to the dimensions of the object under study, and that means X‐rays. It was first established over a century ago that X‐rays could be used to determine molecular structures and X‐rays have since been applied to molecules ranging in size and complexity from table salt to the ribosome, the molecular machine powering protein synthesis in all cells. The first protein structures, myoglobin and haemoglobin, were solved ∼60 years ago. There were just 13 structures in 1976 and 1994 was the first year that over 1000 new structures were deposited in a calendar year. At the time of writing there are over 132 000 PDB entries based on X‐ray data. The explosion in crystallographic analysis can be traced to the development of molecular biology in the 1980s, personal computing and third generation synchrotron light sources in the 1990s.