Proteasomes are the main protein recycling centres in all eukaryotic cells. Apart from their role in maintaining a healthy protein population, these complex molecules are critical as they also control key signals that determine the onset of crucial cellular events, including cell division. However, proteasomes are difficult to study. There are many different proteasome forms in a cell, which are difficult to separate biochemically. Therefore, getting a detailed picture of how exactly a proteasome functions has been difficult, particularly for those complexes that are less abundant but physiologically important.
Ana Toste Rêgo and Paula da Fonseca, of the LMB’s Structural Studies Division, succeeded in using insect cells to produce human proteasomes, of any specific type, suitable for their detailed study. Such approach to the preparation of human proteasomes has been previously unsuccessful. This is because proteasome synthesis is very intricate, with its central core, known as the 20S proteasome, on its own comprising two copies of 14 different proteins that require five additional specialised proteins to coordinate their correct assembly. With their approach, Ana and Paula prepared large amounts of two well-defined proteasome populations: the human 20S proteasome on its own and also together with PA200, a protein found in the nucleus of cells that is known to be a proteasome regulator. The 20S proteasome and PA200 form the 20S-PA200 proteasome complex, one of the so far less studied types of human proteasomes. These complexes were extracted from the insect cells where they were produced and were purified in the laboratory. The proper function of these purified proteasomes was confirmed by biochemical experiments and their structures were solved by state-of-the-art electron microscopy and image processing methods.
The preparation of pure human proteasomes types has significant implications for the understanding of how our cells work and malfunction in disease, and also has the potential for significant contribution to the development of new medicines. Compounds that stop proteasomes from degrading proteins are well established candidates to treat several diseases. There are, at present, three human proteasome inhibitors in clinical use mainly for the treatment of multiple myeloma, while new compounds are being developed both for better anti-cancer treatment and against other varied conditions, including inflammatory disorders.
These studies can also be extended to proteasomes from other organisms, including the malarial parasite. Paula’s group has previously contributed to the demonstration that compounds that suppress the activity of proteasomes have the potential to be developed as a much needed, new generation of antimalarial medicines.
This work was funded by the MRC.
Characterization of fully recombinant human 20S and 20S-PA200 proteasome complexes. Toste Rego, A., da Fonseca, P.C.A. Molecular Cell [Epub ahead of print]
Paula’s group page
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