Archaebacterial proteasome

The 20S proteasome from yeast has a similar overall structure as the archaebacterial proteasome. However, the proteasome from yeast and from higher eucaryotes is composed of seven different a- and P-subrmits that occupy specific positions in the proteasome. By exchange of P-subunits different 20S complexes can form which frmction in specific degradation reactions. The proteasome from yeast and of higher eucaryotes clearly is of a more complicated structure, however it is functionally more versatile than that of archaebacteria and distinct variants of it can be used in specific degradation reactions. 

Dahlmann, B. et al. The multicataly-tic proteinase (prosome, proteasome) comparison of the eukaryotic and archaebacterial enzyme. Biomed Biochim Acta 1991, 50, 465-9. 

The bacterial protease HslVU is unique in two respects at present, it is the only ATP-dependent protease to have atomic coordinates of the full complex determined secondly, and in contrast to all other bacterial ATP-dependent proteases, it contains a proteolytic core that is related to the 20S proteolytic core of archaebacterial and eukaryotic proteasomes. The following sections summarize our understanding of HslVU biochemistry, crystallography, and enzymology and end with some speculation on the implications of these results for other ATP-dependent proteases. 

On the sequence level, HslV shows sequence similarity with the yS-subunits of arch-aebacterial and eukaryotic proteasomes. The crystal structure of E. coli HslV confirmed that individual subunits share the Ntn-hydrolase fold with Thrl at the N-terminus as the nucleophile, just as in proteasomes. Despite these similarities, there are substantial differences between bacterial HslVU and archaebacterial and eukaryotic 20S proteasomes. In contrast to HslVU, 20S proteasomes are assembled from four rings of seven subunits each, that build up a central proteolytic chamber and two flanking antechambers. 

Currently, high-resolution EM image reconstructions for the 26S proteasome (Walz et al. 1998), but no atomic-resolution crystallographic data are available for any complex of 20S proteasomes with ATP-dependent activators. The expected assembly of PAN, the archaebacterial AAA(+) activator of proteasomes (Zwickl et al. 1999) into hexamers suggests a symmetry-mismatched complex in archaebacteria. 

P., and Goldberg, A. L. An archaebacterial ATPase, homologous to ATPases in the eukaryotic 26 S proteasome, activates protein breakdown by 20 S proteasomes. J. Biol. Chem. 1999, 274, 26008-26014. 

Tlie 26S proteasome is composed of two protein aggregates, a 19S and a 20S particle. The main proteolytic component of the 26S proteasome is the 20S particle, the structure of which from an archaebacterial system and a yeast system has been solved (Lowe et al., 1995, Groll et al., 1997). 

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