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Abstract
The 26S proteasome plays an essential role in regulating many cellular processes by the degradation of proteins targeted for breakdown by ubiquitin conjugation. The 26S complex is formed from the 20S core, which contains the proteolytic active sites, and 19S regulatory complexes, which bind to the 20S core to activate it and confer specificity for ubiquitinated protein substrates. We have determined the structure of the human 26S proteasome by electron microscopy and single particle analysis. In our reconstructions the crystallographic structure of each of the subunits of the 20S core can be unambiguously docked by direct recognition of each of their densities. Our results show for the first time that binding of the 19S regulatory particle results in the radial displacement of the adjacent subunits of the 20S core leading to opening of a wide channel into the proteolytic chamber. The analysis of a proteasome complex formed from one 20S core with a single 19S regulatory particle attached serve as control to our observations. We suggest locations for some of the 19S regulatory particle subunits.
Highlights
The eukaryotic 26S proteasome is a multisubunit protein complex responsible for controlled degradation of a wide range of targeted intracellular proteins [1], typically labeled by the covalent attachment of a Lys-48 linked poly ubiquitin chain
Our results show for the first time that binding of the 19S regulatory particle results in the radial displacement of the adjacent subunits of the 20S core leading to opening of a wide channel into the proteolytic chamber
The 26S proteasome is composed of a 20S proteolytic core particle (20S-CP)2 associated with 19S regulatory particles (19S-RPs)
Summary
The eukaryotic 26S proteasome is a multisubunit protein complex responsible for controlled degradation of a wide range of targeted intracellular proteins [1], typically labeled by the covalent attachment of a Lys-48 linked poly ubiquitin chain. This is reflected in the three-dimensional map of the double-capped 26S proteasome presented here, where the density corresponding to each ␣ subunit matches its individual molecular envelope (Fig. 5Bi).
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