X-Ray Crystallography of Biological Macromolecules
Peptides and Proteins
Published Online: 15 SEP 2006
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
Messerschmidt, A. and Huber, R. 2006. X-Ray Crystallography of Biological Macromolecules. Encyclopedia of Analytical Chemistry.
- Published Online: 15 SEP 2006
X-ray crystallography of biological macromolecules comprises the determination of the three-dimensional structures of proteins, nucleic acids and other biological macromolecules at atomic resolution by diffraction of X-rays on crystals of such macromolecules. The atomic structure is obtained from the electron density distribution of the macromolecular crystal, which is the Fourier transform of the waves diffracted by the crystal. The amplitudes of the diffracted waves are determined directly from the diffraction experiment. The diffraction phases are revealed (i) from additional diffraction data of isomorphous heavy atom derivatives [multiple isomorphous replacement (MIR) technique], (ii) from multiple anomalous diffraction (MAD), if suitable anomalous scatterers are in the crystal and using tunable synchrotron radiation, and (iii) by Patterson search techniques (molecular replacement), if structural information on the biological macromolecule under investigation is available. X-ray crystallography of biological macromolecules is the unique method for the elucidation of the spatial structures at atomic resolution of complex biomolecules with molecular masses greater than 30 kDa. The structures represent a time average and spatial average of molecules packed in a crystal. The preparation of suitable crystals may be a limiting factor.