Prokaryotic proteasomes

Song, H., Bochtlee, M., Azim, M., Hartmann, C., Huber, R., and Ramachandean, R. Isolation and characterization of the prokaryotic proteasome homolog HslVU (ClpQY) from Thermotoga maritima and the crystal structure of HslV. Biophys Chem. 2003, 100, 437-452. 

While the efficient assembly of prokaryotic proteasomes proceeds autonomously, assembly of eukaryotic proteasomes appears to require extrinsic maturation factors. The chaperone protein Hsc73 was found to associate with mammalian proteasome precursor complexes, but not with mature proteasomes (Schmidtke et al., 1997). Similarly, Umpl, a small protein contained in half-proteasome precursor complexes of yeast proteasomes, is supposed to have a chaperone-like function. Umpl... 

H. S., and McKay, D. B. Structure and reactivity of an asymmetric complex between HslV and I-domain deleted HslU, a prokaryotic homolog of the eukaryotic proteasome. /. Mol. Biol. 2003, 330, 185-195. 

In this chapter, we review the current knowledge of the structure, assembly and function of the 20S proteasome and its regulators in prokaryotic and eukaryotic cells. 

In addition to the destructive proteolysis processes in the proteasome and lysosome, many constructive proteolysis processes occur in cells. In both prokaryotes and eukaryotes, secreted proteins contain a signal peptide at the N-terminus that directs them to the secretary pathway. This signal peptide must be cleaved later by signal peptidases (typically serine proteases)... 

Prokaryotic counterparts of the ubiquitin pathway and the proteasome Section 23,2.4... 

The Ubiquitin Pathway and the Proteasome Have Prokaryotic Counterparts... 

Both the ubiquitin pathway and the proteasome appear to be pres- ent in all eukaryotes. liomologs of the proteasome are found in prokaryotes, although the physiological roles ot these homologs have not been well established. The proteasomes of some archaea are quite similar in overall structure to their eukaryotic counterparts and similarly have 28 subunits (Figure 23.8). In the archaeal proteasome, however, all a outer-ring subunits and all (8 inner-ring subunits are identical in eukaryotes, each ot or p subunit is one of seven different isoforms. This specialization provides dis-... 

FIGURE 11.3 Comparison of the inhibitory effect of tea polyphenols on chymotrypsin-like activity of the purified proteasomes derived from different sonrces. The chymotrypsin-like activity of the purified proteasomes recombinant prokaryotic 20S proteasome, enkaryotic 20S proteasome, and eukaryotic 26S proteasome were analyzed by incnbation with the fluogenic substrate Suc-Leu-Leu-Val-Tyr-AMC (for chymotrypsin-like activity of the proteasome) in the presence of the tea polyphenols (5 pM) for 30 min and detected free AMC groups. Assays were performed in triplicate, and the results of representative experiments are shown as mean SD. 

Theaflavins efficiently and specifically inhibited the proteasomal chymotrypsin-like activity of the purified mammalian 20S and 26S proteasomes in cell-free systems (figure 11.3) as well as 26S proteasomes in tumor cell extracts (table 11.1). The purified M. thermophila recombinant 20S proteasome was more sensitive to theaflavins than mammalian 20S or 26S proteasomes, possibly due to prokaryotic recombinant 20S proteasome without postmodification that forms steric hindrance that prevents theaflavins from binding to the chymotrypsin-like activity subunit of the 20S proteasome. When assaying for proteasomal chymotrypsin-like activity in human cancer cell extracts, the IC50 values of tea polyphenols were apparently increased compared... 

Proteasomes are found in both prokaryotes and eukaryotes, and specific pathways exist to target a protein so that it complexes with a proteasome and is degraded. 

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... 

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). 

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