Protein structures made crystal clear
The determination of the structure of protein crystals involves the formation of the native protein and of an isomorphous heavy atom derivative of the protein. The derivative is a crystal structure identical to the native protein except for the presence of heavy atoms bound to protein molecules. This crystallisation is difficult to accomplish and is often the limiting step in crystal structure determination. A new device for crystal derivative formation with rare or toxic gases such as Xenon and Krypton has been developed. The instrument consists of a piston, which pressurises the gas being used up to 100bar. A standard cryo loop on a special pin is used to pick up the native crystal from its cryo protectant. Following this the pin, which is attached to a pin holder, clips into the instrument. The crystal is then pressurised as the derivative is formed using gases. The derivative is then freeze-trapped in order to prevent the desorption of the bound gases. Furthermore, the gas is fully confined so that expensive gases can be used without the need to replenish the supply. The instrument is fully automated to give ease of operation. It also allows reproducible conditions to be obtained from experiment to experiment with regard to parameters such as pressure and time of exposure of the native crystal to the gas. A laboratory prototype has been developed and partners are sought for further development.
