Dissecting the assembly pathway of the 20S proteasome

AbstractProteasomes reach their mature active state via a complex cascade of folding, assembly and processing events. The Rhodococcus proteasome offers a means to dissect the assembly pathway and to characterize intermediates; its four subunits (α1, α2, β1, β2) assemble efficiently in vitro with any combination of α and β. Assembly studies with wild-type and N-terminally truncated β-subunits in conjunction with refolding studies allowed to define the role of the propeptide which is two-fold: It supports the initial folding of the β-subunits and it promotes the maturation of the holoproteasomes

Decelerated degradation of short peptides by the 20S proteasome

AbstractBased on a twelve residue master peptide comprising all five specific cleavage sites defined for the proteasome, a set of variant peptides was generated in order to probe specificity and to elucidate the mechanism which determines product size. It is shown that the rate of degradation by the 20S proteasome from Thermoplasma acidophilum depends critically on the length of the peptide substrate. Peptides of 14 residues and longer are degraded much faster than shorter peptides although the sites of cleavage remain unchanged. The decelerated degradation of peptides shorter than 14 residues explains the accumulation of products with an average length of seven to nine residues

The proteasome: Paradigm of a self-compartmentalizing protease

and unfolding are closely related mechanistically, it is assumed, but not proven, that this task is performed by ATPase complexes, which bear some resemblance to the chaperonins and have been referred to as “reverse chaperones ” or “unfoldases ” (Lupas et al., 1993). Since their action requires the hydrolysis of ATP, protein degradation becomes energy-dependent, although the hydrolysis of the polypeptide chain itself is an exergonic process. Self-compartmentalizing proteases are common in all three domains of life: archaea, bacteria, and eukarya. This bears testimony to an old evolutionary principle. In fact, contrary to organelles such as the lysosome, self-compartmentalizing molecular devices offer far greater flexibility: when equipped with the appropriate localiza