Background (by Bernhard Rupp)

What is X-ray Crystallography ?

X-ray crystallography is an experimental technique that exploits the fact that X-rays are diffracted by crystals. It is not an imaging technique. X-rays have the proper wavelength (in the ?ngstr?m range, ~10-8 cm)  to be scattered by the electron cloud of an atom of comparable size. Based on the diffraction pattern obtained from X-ray scattering off the periodic assembly of molecules or atoms in the crystal, the electron density can be reconstructed. Additional phase information must be extracted either from the diffraction data or from supplementing diffraction experiments to complete the reconstruction (the phase problem in crystallography). A model is then progressively built into the experimental electron density, refined against the data and the result is a quite accurate molecular structure.

Why Crystallography ?    

The knowledge of accurate molecular structures is a prerequisite for rational drug design and for structure based functional studies to aid the development of effective therapeutic agents and drugs. Crystallography can reliably provide the answer to many structure related questions, from global folds to atomic details of bonding. In contrast to NMR, which is an indirect spectroscopic method, no size limitation exists for the molecule or complex to be studied. The price for the high accuracy of crystallographic structures is that a good crystal must be found, and that limited information about the molecule's dynamic behavior in solution is available from one single diffraction experiment. In the core regions of the molecules, X-ray and NMR structures agree very well, and enzymes maintain their activity even in crystals, which often requires the design of non-reactive substrates to study enzyme mechanisms.

5. Methods (From Wikipedia, the free encyclopedia)

5.1 Crystallization

5.2 Data collection

5.2.1 Mounting the crystal

5.2.2 X-ray sources

5.2.3 Recording the reflections

5.3 Data analysis

5.3.1 Crystal symmetry, unit cell, and image scaling

5.3.2 Initial phasing

5.3.3 Model building and phase refinement

5.4 Deposition of the structure

Protein crystallography

Tutorials

Primary databases

Derivative databases

Springer Protocols: Abstract: Preparation of DNA-Protein Complexes ...

Although a plethora of techniques is now available to study DNA-protein interaction, none provides detailed structural information at the molecular level ...

Protein:DNA Interaction Group

extensive surface for mediating protein-protein interactions. .... microscopy and X-ray crystallography. In the last year we have been able to purify the ...
www.embl-grenoble.fr/groups/dna/rr03_94.pdf

Identification of DNA Recognition Sequences and Protein ...

meric and heteromeric protein-protein interaction and DNA-. protein interaction. ..... demonstrated by EMSA and X-ray crystallography of single- ...
mcb.asm.org/cgi/reprint/18/11/6447.pdf

Structure determination techniques - X-ray and NMR

Protein secondary structure, DNA double helix and RNA stem and loop ... X-ray crystallography requires the growth of protein crystals up to 1 mm in size ...
www.whatislife.com/reader/techniques/techniques.html