Crystallisation

Crystallisation as a purification technique has long been used by investigators and industrialists in the small-molecule field, but has largely been ignored until recently in the biologics field. With increasing product yields and concentrations, this approach is now attracting much interest as an alternative to some chromatographic steps, thereby reducing the number of these required. Crystallisation of proteins has long been used in structural analysis studies where screens have been developed to find conditions that allow the successful crystallisation of a target protein. Now the potential of this approach in downstream processing is being seriously considered and has been used during the purification of glucose isomerase and insulin. A number of investigators have now reviewed the principles of protein crystallisation and the technical aspects of process development for its large-scale use. Despite the promise of this approach, there are still scale-up issues involved in further developing this technique and a lack of process development in the area. The development of novel microanalysis methods to determine large-scale conditions that will drive crystallisation of the target protein of interest at high yield is currently under way and may help overcome such limitations. Hence there is the potential to develop low-cost methods of purification that utilise crystallisation for many biologics, although currently this potential is largely unrealised.