The proteasome and the degradation of oxidized proteins: Part I—structure of proteasomes☆

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Abstract

The main machinery responsible for cellular protein maintenance is the ubiquitin-proteasomal system, with its core particle the 20S proteasome. The main task of the system is a fast and efficient degradation of proteins not needed anymore in cellular metabolism. For this aim a complex system of regulators evolved, modifying the function of the 20S core proteasome. Here we summarize shortly the structure of the 20S proteasome as well as its associated regulator proteins.

Abstract

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Highlights

► Form and function of the 20S proteasome are described. ► Comparison between Archaeal and eukaryotic 20S proteasome are pointed out. ► Structure and function of proteasomal regulators are highlighted.

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Most cited references 30

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A gated channel into the proteasome core particle.

M Groll, M Bajorek, A. Köhler … (2000)

The core particle (CP) of the yeast proteasome is composed of four heptameric rings of subunits arranged in a hollow, barrel-like structure. We report that the CP is autoinhibited by the N-terminal tails of the outer (alpha) ring subunits. Crystallographic analysis showed that deletion of the tail of the alpha 3-subunit opens a channel into the proteolytically active interior chamber of the CP, thus derepressing peptide hydrolysis. In the latent state of the particle, the tails prevent substrate entry by imposing topological closure on the CP. Inhibition by the alpha-subunit tails is relieved upon binding of the regulatory particle to the CP to form the proteasome holoenzyme.

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Docking of the proteasomal ATPases' carboxyl termini in the 20S proteasome's alpha ring opens the gate for substrate entry.

David Smith, Shih-Chung Chang, Soyeon Park … (2007)

The 20S proteasome functions in protein degradation in eukaryotes together with the 19S ATPases or in archaea with the homologous PAN ATPase complex. These ATPases contain a conserved C-terminal hydrophobic-tyrosine-X motif (HbYX). We show that these residues are essential for PAN to associate with the 20S and open its gated channel for substrate entry. Upon ATP binding, these C-terminal residues bind to pockets between the 20S's alpha subunits. Seven-residue or longer peptides from PAN's C terminus containing the HbYX motif also bind to these sites and induce gate opening in the 20S. Gate opening could be induced by C-terminal peptides from the 19S ATPase subunits, Rpt2, and Rpt5, but not by ones from PA28/26, which lack the HbYX motif and cause gate opening by distinct mechanisms. C-terminal residues in the 19S ATPases were also shown to be critical for gating and stability of 26S proteasomes. Thus, the C termini of the proteasomal ATPases function like a "key in a lock" to induce gate opening and allow substrate entry.

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The proteasomal system.

Tobias Jung, Betul Catalgol, Tilman Grune (2009)

Rising interest in the mechanism and function of the proteasomes and the ubiquitin system revealed that it is hard to find any aspect of the cellular metabolic network that is not directly or indirectly affected by the degradation system. This includes the cell cycle, the "quality control" of newly synthesized proteins (ERAD), transcription factor regulation, gene expression, cell differentiation, immune response or pathologic processes like cancer, neurodegenerative diseases, lipofuscin formation, diabetes, atherosclerosis, inflammatory processes or cataract formation and in addition to that the aging process itself and the degradation of oxidized proteins, in order to maintain cell homeostasis. But also this seems to be only a small aspect of the general view. The various regulator proteins that are able to change the rate or specificity of proteolysis, fitting it out for highly specialized tasks, or the precise regulation of the half-life of cellular proteins by ubiquitin-mediated degradation shape the proteasome and the ubiquitin-proteasome system into a fascinating and essential part of cellular function in the three kingdoms of bacteria, plants and animals. This review tries to summarize the current knowledge on the proteasome and the ubiquitin-proteasomal system, including the cellular functions of this system.

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Author and article information

Contributors

Tilman Grune

Journal

Journal ID (nlm-ta): Redox Biol

Journal ID (iso-abbrev): Redox Biol

Title: Redox Biology

Publisher: Elsevier

ISSN (Electronic): 2213-2317

Publication date PMC-release: 19 January 2013

Publication date (Electronic): 19 January 2013

Publication date Collection: 2013

Volume: 1

Issue: 1

Pages: 178-182

Affiliations

Department of Nutritional Toxicology, Institute of Nutrition, Friedrich Schiller University Jena, Dornburger Str. 24, 07743 Jena, Germany

Author notes

[* ]Corresponding author. Tel.: 49 3641949671; fax: +49 3641949672. tilman.grune@ 123456uni-jena.de

Article

Publisher ID: REDOX24

DOI: 10.1016/j.redox.2013.01.004

PMC ID: 3757679

PubMed ID: 24024151

SO-VID: eef98b50-dfec-48d9-9f9a-c480bf3197a7

License:

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

History

Date received : 1 January 2013

Date revision received : 9 January 2013

Date accepted : 10 January 2013

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