Illustrating macromolecule crystallisation quality
Information on the majority of protein structures known today has been produced using X-ray crystallography, also called X-ray diffraction. An X-ray beam is directed at solid crystals containing trillions of identical molecules of interest. A computer programme creates a three-dimensional (3D) image from position calculations of every atom in the molecule based on the detected diffraction pattern. Growing high-quality crystals is a complicated and delicate process that can take months or even years with inferior outcomes in many instances. Scientists exploited a novel technique to detect the quality of crystal nucleation early with EU funding of the project 'Novel tools for crystallisation of macromolecules' (TOPCRYST). Their aim is to enable early detection of protein crystal quality to minimise loss of time, effort and money in the case of poor nucleation. The dual polarisation interferometry (DPI) technique, developed by TOPCRYST for studying molecular structures and interactions, uses an optical waveguide with light in its core. Any changes in molecule interactions on the waveguide surface are reflected in changes in the light propagation within the waveguide. Scientists used three molecular system models whose crystallisation conditions are well characterised and are therefore often employed to test new methods. A crystallisation 'signature' or signal pattern occurring only upon successful crystallisation was thus identified and used to define crystallisation conditions for two historically problematic proteins. In addition, a novel crystallisation condition was identified for one of the model proteins. TOPCRYST thus demonstrated the effectiveness of real-time DPI monitoring in identifying successful crystallisation conditions for macromolecules of interest with significant reduction in time and effort. Increasingly successful structural studies due to this technique are expected to have broad-sweeping impact on drug discovery and health care.
