How Size Exclusion Chromatography Illuminates Protein Crystallisation

Understanding membrane protein crystallisation is one of the main goals of molecular biology studies aimed at the structural characterisation of proteins. Now, work performed by Malvern Instruments in conjunction with the Membrane Protein Laboratory at London’s Imperial College, has been published as an application note which outlines a method capable of providing insight into the likelihood of crystallisation of a sample and its protein content. ‘Analysis of membrane protein by multi-detector SEC’ describes how the Viscotek TDAmax size exclusion chromatography (SEC) system was used to characterise and optimise the proportion of protein and detergent in a purified membrane protein sample.

Crystallization of a membrane protein can depend on many factors, such as protein purity and the detergent concentration or type. Removing too much of the detergent component of a membrane protein complex can lead to degradation of the protein and reduce the chances of crystallisation.

In this application note, the protein detergent complex (PDC), a bacterial membrane protein involved in multidrug resistance, is characterised using the Viscotek TDAmax system, a complete size-exclusion chromatography system with refractive index (RI), ultraviolet (UV), light scattering (LS) and intrinsic viscosity (IV) detectors. The molecular weight of the PDC and of the free detergent n-dodecyl β-D-maltoside (DDM) micelles was measured. Furthermore, the composition of the PDC, in terms of protein and DDM content, was measured and found to be very close to expectations. Size Exclusion Chromatography is the technique of choice for rapid and reliable characterisation of molecular weight and molecular structure for all types of macromolecules, including proteins.