Proteasome core particle

Three other components that my laboratory has identified and partially purified from Fraction 2 of reticulocytes, termed CF1-CF3, are involved in the degradation of proteins ligated to ubiquitin [24]. These are apparently subcomplexes of the 26S proteasome, a large ATP-dependent protease complex first described by Re-chsteiner and co-workers [25], CF3 is identical to the 20S proteasome core particle [26], while CFl and CF2 may be similar to the base and lid subcomplexes of the 19S regulatory particle of the 26S proteasome, described more recently by the Finley laboratory [27], In hindsight, the reason for finding subcomplexes, rather than the complete 26S complex in Fraction 2 was technical we have routinely prepared Fraction 2 from ATP-depleted reticulocytes [20], under which conditions the 26S proteasome dissociates to its subcomplexes. We found that incubation of the three subcomplexes in the presence of ATP promotes their assembly to the 26S proteasome [24, 26]. The role of ATP in the assembly of the 26S proteasome complex remains unknown. 

Kohler, A., Cascio, P., Leggett, D. S., Woo, K. M., Goldberg, A. L., and Finley, D. The axial channel of the proteasome core particle is gated by the Rpt2 ATPase and controls both substrate entry and product release. Molecular Cell 2001, 7, 1143-1152. 

Groll, M., Bajorek, M., Kohler, A., Moroder, L., Rubin, D. M., Huber, R., Glickman, M. N., and Finley, D. A gated channel into the proteasome core particle. Nat. Struct. Biol. 2001,... 

M. Groll and R. Huber. Substrate access and processing by the 20S proteasome core particle, bit. J. Biochem. Cell. Biol., 35 606-616, 2003. 

Jager, S., Groll, M., Huber, R., Wolf, D. H., and Heinemeyer, W. Proteasome beta-type subunits unequal roles of propeptides in core particle maturation and a hierarchy of active site function./. Mol. Biol. 1999, 291, 997-1013. 

Ubiquitinated proteins are degraded by a large com-plex known as the 26S proteasome (Afr 2.5 X 106) (Fig. 27-42). The proteasome consists of two copies each of at least 32 different subunits, most of which are highly conserved from yeasts to humans. The proteasome contains two main types of subcomplexes, a barrellike core particle and regulatory particles on either end of the barrel. The 20S core particle consists of four rings the outer rings are formed from seven a subunits, and the inner rings from seven /3 subunits. Three of the... 

In terms of structure and function, the 265 proteasome is an ATP-dependent multicatalytic enzyme complex comprising one or two 195 regulatory caps and a proteolytic 205 core particle within which protein degradation occurs.18,25,26 The 205 proteasome contains three pairs of proteolytic subunits, (35, (32 and (31, for which chymotrypsin-like (CT-L), trypsin-like (T-L) and caspase-like (C-L) activities have been ascribed, respectively, based on their substrate preferences.27... 

To degrade proteins they must be unfolded before to be able to enter the 20S proteolytic core particle. Generally speaking, oxidized, therefore partially unfolded proteins, are better substrates for the proteasome, in comparison to native, normal folded... 

The multicatalytic protease complex consists of a proteolytically active central core (core particle, 20S proteasome) and of a 19S regulatory complex which is attached to the core particle and is responsible for substrate recognition and unfolding. The spatial structure and the en2ymatic mecha-... 

FIGURE 27-42 Three-dimensional structure of the eukaryotic proteasome. The 25S proteasome is highly conserved in all eukaryotes. The two subassemblies are the 20S core particle and the 1 9S regulatory particle, (a) (PDB ID 1 IRU) The core particle consists of four rings arranged to form a barrel-like structure. Each of the inner rings has seven different fj subunits (light blue), three of which have protease... 

Proteasomes are expressed almost ubiquitously throughout the kingdoms of hfe, and the overall shape of the 20S core particles in which the proteolytic proteasome activities reside is highly conserved. Prokaryotic 20S proteasomes are C2-symmetrical barrel-shaped particles assembled in four stacked rings of seven proteins each (Figure 12.1). The two outer rings are composed of seven... 

Immunoproteasome Constitutive proteasome Figure 12.1 Evolution of proteasome 20S core particles. 

Proteasomes are multisubunit peptidases found in all eukaryotes and archaea and some bacteria. The 20 S proteasome is found only in actinomycetales. Prokaryotic 20 S proteasome cores are self-compartmentalized peptidases composed of 14 a-subunits and 14 P-subunits, with the N-terminal threonines of the P-subunits providing the protease activity. Core particles from archaea and bacteria are simpler structures with homoheptameric rings of catalytic P-subunits flanked by homoheptameric rings of a-subunits. In bacteria, proteasomes are evolved in protein turnover, but in archaea, their function is unknown. Proteasomes are threonine peptidases (Darwin 2009 Murata et al. 2009). 

Fig. 9 (continued) assignments of correlations from the complex are not available, (b) Residues whose resonances are affected by the IIS interaction are mapped on the proteasome structure, (c) Crystal structure of the llS-proteasome complex, (d) The intensities of resonances during the titration are used to obtain an approximate dissociation constant (irD = 12 10 pM) for the IIS interaction that is consistent with the core particle titration data (see insets). The decrease in intensity of one of the correlations from L81 is shown on the left and the concomitant increase in a bound peak on the right. Errors are quantified from signal-to-noise in spectra. [Ligand] and [Protein] refer to total ligand and protein concentrations. Adapted from [3] with permission... 

The functional proteins in the cell have to be protected in order to prevent premature degradation. Some of the intracellularly active proteolytic enzymes are therefore enclosed in lysosomes (see p. 234). The proteinases that act there are also known as cathepsins. Another carefully regulated system for protein degradation is located in the cytoplasm. This consists of large protein complexes (mass 2 10 Da), the proteasomes. Proteasomes contain a barrel-shaped core consisting of 28 subunits that has a sedimentation coef cient (see p. 200) of 20 S. Proteolytic activity (shown here by the scissors) is localized in the interior of the 20-S core and is therefore protected. The openings in the barrel are sealed by 19-S particles with a complex structure that control access to the core. 

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