The importance of developing miniaturised and automated assays for the crystallisation of biological macromolecules

Fabrice Gorrec, MRC-LMB, Cambridge, UK

X-ray crystallography still plays a dominant role in solving biomolecular structures. Collaborations with structural biologists are encouraged now that only small amounts of protein are required and the process of structure determination is efficient enough for the majority of biologists and biochemists to employ it. Numerous innovations and technological developments have assisted progress in BioMolecular Crystallography (BMC), notably in the fields of molecular biology, IT and synchrotron light sources.

BMC will ultimately always depend on the production of quality crystals. Crystallisation had become the bottleneck of the structure determination process due to the increasingly challenging nature of novel biological samples of interest. When X-ray structure determination evolved into a standard technique for researchers to apply to their favoured proteins, crystallisation became a problem and has now evolved into a science in itself. Nevertheless, the approach is still empirical: at the time of the crystallisation experiments, nothing is known about the biomacromolecule to be assembled into an ordered periodic crystal lattice. The challenge for crystallographers is how to solve a puzzle without knowing the shape of the main pieces.

Beyond crystallisation, one has to look at the BMC process overall, with its multitude of steps, each one of which is potentially a dead-end. The worst is late stage failure (failure to analyse diffraction data because of “the phase problem” is frequent). A parallel approach is strongly recommended, with different trials at each stage of the process in anticipation of the difficulties that one could confront in the next stage. In addition to multiple sample variants, one will employ a variety of crystallisation screens.

There are an almost infinite number of parameter combinations when attempting to solve a structure. Most of these parameters alter the availability and quality of the required crystals. A challenging crystal structure generally results from thousands – or hundreds of thousands – of crystallisation assays in initial screening and optimisation experiments. This volume has driven developments in automation and miniaturisation.

Miniaturisation enables the use of a multitude of crystallisation conditions even when the amount of sample is limited. Automation enables one to proceed quickly, accurately and effectively. Speed is important because samples typically have poor stability. Ensuring accuracy and repeatability reduces eventual reproducibility issues to a minimum (optimising with a subsequent batch of protein or a sample that is not freshly prepared frequently results in failure). Finally, cost-effectiveness is particularly relevant for difficult, long-term, projects. It is hard to imagine the process of structure determination can be fully automated soon, because of its complexity and the level of know-how required for each step. Nevertheless, hands-free macromolecular crystallisation in nanolitre drops has already been successfully enabled with commercially available robots (Figure 1).




Figure 1. Fully automated system for high-throughput crystallisation in nanolitre drops. The plates containing the crystallisation conditions are laid on the deck of a liquid handling robot with a customised aluminium lid on top. A gripper removes the lid and places a plate on the deck of the mosquito® Crystal robot for setting up nanolitre drops. The plate is later transported to a sealer (for sealing with transparent tape). Finally, the plate is placed back onto its original location (crystallisation experiments start).





Fabrice Gorrec gained experience in Structural Biology and Drug Discovery at GlaxoSmithKline (2003-4) and later at the Structural Genomics Consortium (2005-6). Since 2007, Fabrice has been responsible for the Macromolecular Crystallisation Robotic Facility at the Medical Research Council – Laboratory of Molecular Biology (MRC-LMB, Cambridge, UK). He works with research scientists to enable extensive initial crystallisation screening and later crystal optimisation, always lending his support to tackling difficult, long-term research problems. In 2012, Fabrice received an MRC Award for innovations in the field of macromolecular crystallisation.

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