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Structural BiologyPart of Biological Sciences

Protein production

Solving biomolecular structures requires pure samples that remain stable during the processes of crystallisation or NMR data collection. Most proteins are expressed in bacteria and purified from the bacterial 'soup' using affinity chromatographic techniques.

Making molecules as complicated as proteins is impossible for even an expert chemist so we employ living systems, bacteria, to carry out the task for us. The gene encoding your protein is transformed into a strain of E. coli which is grown in culture flasks in the protein production laboratory. Protein expression is initiated by the addition of an inducing agent. The cells are finally collected by centrifugation and their contents released using sonication or homogenisation.

Protein purification columns; nickel affinity (left) and ion exchange (right)
Protein purification columns

At this point you have your protein in a 'soup' of E. coli proteins so we need to find a way to lose all but our protein of interest. There are many ways of achieving this but methods today employ affinity tag purifications whereby the protein has an attached sequence of amino acids which specifically bind a certain type of chemical resin . The most common is the histidine tag which binds nickel affinity resins. Only your protein of interest binds while the E coli proteins wash through.

Some contamination always persists so additional chromatography methods such as ion exchange, and gel filtration can be used to obtain a pure sample of your protein.

Columns of these resins (see image) are attached to liquid chromatography systems which pump solutions through a flow path which handles protein loading, buffer mixing, protein detection using UV light and fraction collecting to isolate the pure protein as it elutes from the system.

All of ths equipment is available at the Centre for Biological Sciences.

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