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.
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The
author regrets that unexpected events have forced him
to cancel his attendance and this presentation. |
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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
E-mail: walz@mozart.biochem.mpg.de
WWW: www.biochem.mpg.de/~walz
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