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The 26S proteasome—a macromolecular assembly with proteolytic activity

Jochen Walz*, Abraham J.Koster, Mary Kania, Annette Erdmann, Dieter Typke, Reiner Hegerl, Wolfgang Baumeister

Molecular Structural Biology
Max-Planck-Institute for Biochemistry
This is an abstract for a poster to be presented at the Fifth Foresight Conference on Molecular Nanotechnology.

The author regrets that unexpected events have forced him to cancel his attendance and this presentation.

The 26S proteasome is a biological macromolecule consisting of a variety of different subunits. The complex is ubiquitous in eukaryotic cells, working as natural machinery for degradation of proteins. Regarding the structure as well as the function of the 26S proteasome, the macromolecule can be subdivided into two parts. Four ring-like structures form the 20S proteasome, a cylindrically shaped molecule with a length of 15 nm and a diameter of 11 nm, enclosing three cavities. The central cavity contains the active sites of the proteasome, where peptide chains are cleaved into oligomers. Attached to the 20S core particle are one or two so-called 19S complexes, resulting in a length of 30 nm or 44 nm for the entire particle. It is assumed, that it contains the substrate binding site, recognizing proteins subjected to degradation. Additionally, a protein has to be unfolded prior to cleavage, because only the unfolded peptide chain can enter the reaction compartment of the 20S core.

For investigation of the structure and thereby the function of biological macromolecules in the size range of the 26S proteasome, transmission electron microscopy has turned out to be the method of choice. The sensitivity of the objects to the electron beam allows imaging only with a low dose, resulting in a high noise level in the images. Heading for higher resolution, one has to image multiple copies of the object and average the images after alignment to a common origin. With images of the object in different orientations, the tomographic approach of optical sectioning can be used to calculate the three-dimensional density distribution.

*Corresponding Address:
Jochen Walz, Max-Planck-Institute for Biochemistry
Am Klopferspitz 18a, 82152 Planegg-Martinsried, Germany
telephone: +49-89-8578-2635, fax: +49-89-8578-2641
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