Protein Crystallography2018-11-14T11:51:56+00:00

Stable purified proteins enter into our crystallisation screening process. This begins with the use of sparse matrix crystallisation screens along with relevant screens designed around any literature precedents. Tool compounds are utilised, where available, to explore the options for co-crystallisation.

An initial hit from these screens may need further optimisation to improve the size and quality of diffraction of the crystal. We have an accumulated knowledge of numerous useful tips and tricks to apply at this stage.

What we aim for in a crystallisation drop is a number of individual, regular crystals measuring at least 50mm in all 3-dimensions. What we actually see however can vary from clear drops to bulk precipitate and “skin” formation to well-ordered crystals. Between these extremes, irregular, twinned, micro, multiple and needle-like crystals can be obtained that provide initial “hits” suitable for further optimisation.

Factors which have an effect on the crystallisation process are numerous and can be very loosely grouped as those associated with the protein sample, with the precipitant or with the experimental set-up.

There are three key areas to consider when optimising crystal quality. Firstly, the protein itself where purity, concentration, stability and buffer can all impact the crystal generation.

Secondly, the chemical components (precipitant) used in a screen which gives rise to a crystal. Varying the polymer chain length, anions or cations in the salts and pH are all important variables to test. Thirdly, how the experiment is set-up can greatly alter the formation of crystals. We use a number of different formats such as sitting or hanging drops, in gels, lipidic cubic phases, robotically at nL up to mL scale and at different temperatures. Seeding from initial crystal hits can produce dramatic improvements in quality as well as new crystal forms.

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