Imperial College London,
South Kensington Campus,
London SW7 2AZ,
tel: +44 (0)20 7589 5111
X-Ray Crystallography Introduction
X-ray crystallography is a technique for solving the 3-dimensional structures of macromolecules from single crystals. Many of the structures shown in our picture gallery were obtained by X-ray crystallography. This method is widely used to study the structures of proteins, DNA, complexes of proteins with drugs, inhibitors, substrates, other proteins and nucleic acids. The three dimensional structure can be used to understand how a protein functions: it is an essential component in understanding the mechanism, inhibition and mutagenesis data for a protein.
If you are interested in solving a structure the following steps will generally be necessary:
Purify your macromolecule or complex in milligram quantities (usually 10 - 100 mgs are needed).
Concentrate the protein to around 5 - 20 mg/ml.
Screen for suitable crystallisation conditions using sparse matrix screen kits and robots to produce crystallisation trial drops in the 200 nl range.
Optimize the crystallisation conditions to give crystals that give good quality diffraction.
Obtain a data set consisting of images of the diffraction pattern taken with the crystal at different orientations.
Derive a list of diffraction spots and their intensities.
Solve the Phase problem and calculate an electron density map.
Build the structure of the macromolecule into the electron density map.
Refine the structure to ensure the best fit between the model and the density.
Data collection for X-ray crystallography can be performed either on an in house system such as the one available at Imperial College. Alternatively, if crystals are small or poorly diffracting then after initial screening on the in house source, data can be recorded at a synchrotron. We have group time available at the Synchrotron Radiation Source, in Daresbury. This time is available to Imperial College Crystallographers. See the web page for available slots and contact Jeremy to book time.
If you are interested in using the facility please contact Professor So Iwata, the CSB Director or Dr Jeremy Moore , The Facility Manager.
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