Evolution of Proteasomal Subunits

Since the a - and P-subunits of the Thermoplasma proteasome share 26 sequence identity, it was not unexpected that they have the same 3-dimensional fold.28 Most likely the two genes arose by duplication of one primordial gene.34 This gene was probably the proteolytically active P-subunit, as no catalytic activity has been established for the a-subunits, (except for the proposed RNase activity of one of the a-subunits50 which awaits further confirmation). Mutations in the proregion of a...

Entry of Substrates Processive Degradation and Length of Cleavage Products

Degradation of proteins by 20S proteasomes requires their complete unfolding. This reflects the restriction of substrate passage through the narrow channels separating the three proteasomal cavities. Entry of an unfolded protein substrate through the lateral gate formed by the a subunit ring could be visualized for the Thermoplasma proteasome.49 Nanogold-labeled insulin P chain molecules got stuck with their bulky 2 nm gold moiety at the a rings. Digests of oxidized insulin P chain and...

Relationship Between Topography and Functions of Subunits

In what respect is the model of the architecture of the human 20S proteasome compatible with biological and biochemical features that are known from other experiments Most knowledge about functions of individual proteasome subunits have been obtained from yeast mutants defective in some of the proteolytic activities. For instance, mutation of the genes Prel and Pre2, which encode for yeast proteasome subunits homologous of human C7I and MB1, have been found to result in reduction or loss of...

The HslVU Protease Complex

Unlike the actinomycetes, which contain genuine proteasomes, other bacteria have a more distantly related complex called HslVU (also termed ClpQY) (Table 2.2). This ATP-dependent protease is a two-component multimeric complex composed of the pro-teolytic component HslV (ClpQ), whose primary sequence is highly similar to P-type proteasome subunits,16,41 and HslU (ClpY), a member of the Hsp100 Clp family of ATPases.42,43 In vivo, HslV and HslU form a complex, which is induced, along with the...

Active Sites in the Yeast 20S Proteasomes

Based on sequence comparisons, eukaryotic 20S proteasomes with their seven different a and P type subunits were predicted to contain only three pairs of active P type subunits bearing a catalytic center corresponding to that identified in the archaebacterial proteasome.25 The critical residues supposed to be essential for active site formation in the Thermoplasma P subunit, in particular thrj, glu17, lys33, serj29, aspj66, are present (except that glu17 is replaced by aspj7) in all known...

Purification of Proteasomes from Arpn10 Mutants

The functional dissection of large protein complexes such as the RP has often been accomplished through the definition of discrete subcomplexes. By characterizing the biochemical activities of individual subcomplexes, the steps in the reaction pathway can be resolved from one another, studied in isolation, and mapped to specific subunits. It is well established that the proteasome can be dissociated into two subcomplexes the CP and the RP. The resolution of two structural domains in the RP...

The Structure Mechanism and Assembly of Prokaryotic Proteasomes

Pyrococcus Furiosus Detail

The Thermoplasma proteasome is a cylinder-shaped particle built by four seven-membered rings (Fig. 2.1B).26 Each of the two outer rings are formed by seven identical a-subunits, and the two inner rings by seven identical P-subunits.27 The 3-dimensional structures of the a- and P-subunits are similar, i.e., two central five-stranded P-sheets are flanked on either side by a-helices.28 It came as a surprise that the proteasome's catalytic mechanism is unlike that of any other known protease. The...

Dieter H Wolf

Prot Asomes

Proteasomes, the world of regulatory proteolysis surprise and astonishment has struck the scientific community when the structural complexity and principal functions of these large proteinase particles became apparent. From degradation of malfolded proteins, antigen generation, regulatory adaptation, to control of cell cycle the functions of proteasomes are numerous, and many surprises may lie still ahead of us. For a long time researchers had resented the idea that proteinases could be...

The Function of Proteasomal Propeptides

In line with propeptide functions in other proteinases, proteasomal propeptides may exert an inhibitory function by preventing gain of premature proteolytic activity and a chaperoning function by assisting the correct, incorporation-competent folding of the subunit. One might also imagine a targeting function to ensure the correct localization of the given subunit in the complex, and finally, interactions of propeptides with other subunits or components aiding the eukaryotic core particle...

Claudia Hartmann Anja Dorowski Robert Huber and Michael Groll

Many cellular processes, including stress response, cell cycle control and metabolic adaptation require protein turnover. The diversity of proteins that have to be degraded contrasts with the comparatively small number of proteases that are involved in this process.1 Due to their broad substrate specificity, the activity of these proteases has to be tightly controlled. Therefore, they are either confined to organelles like the vacuole lysosome,2 or they form sequestered compartments themselves,...