Proteasomes: multicatalytic proteinase complexes (original) (raw)
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Prosomes and their multicatalytic proteinase activity
European Journal of Biochemistry, 1992
Prosomes were first described as being mRNA-associated RNP (ribonucleoprotein) particles and subcomponents of repressed mRNPs (messenger ribonucleoprotein). We show here that prosomes isolated from translationally inactive mRNP have a protease activity identical to that described by others for the multicatalytic proteinase complex (MCP, 'proteasome'). By RNase or non-ionic detergent treatment, the MCP activity associated with repressed non-globin mRNP from avian erythroblasts, sedimenting at 35 S, could be quantitatively shifted on sucrose gradients to the 19-S sedimentation zone characteristic of prosomes, which were identified by monoclonal antibodies. The presence of small RNA in the enzymatic complex was shown by immunoprecipitation of the protease activity out of dissociated mRNP using a mixture of anti-prosome monoclonal antibodies; a set of small RNAs 80-120 nucleotides long was isolated from the immunoprecipitate. Furthermore, on CsCl gradients, colocalisation of the MCP activity with prosomal proteins and prosomal RNA was found, and no difference in the prosomal RNA pattern was observed whether the particles were fixed or not prior to centrifugation. These data indicate that the MCP activity is a property of prosomes, shown to be in part RNP and subcomplexes of in vivo untranslated mRNP. A hypothesis for the role of the prosome-MCP particles in maintaining homeostasis of specific protein levels is proposed.
Biochemical Journal, 1993
The multicatalytic proteinase complex or proteasome is a high-molecular-mass multisubunit proteinase which is found in the nucleus and cytoplasm of eukaryotic cells. Electron microscopy of negatively stained rat liver proteinase preparations suggests that the particle has a hollow cylindrical shape (approximate width 11 nm and height 17 nm using methylamine tungstate as the negative stain) with a pseudo-helical arrangement of subunits rather than the directly stacked arrangement suggested previously. The side-on view has a 2-fold rotational symmetry, while end-on there appears to be six or seven subunits around the ring. This model is very different from that proposed by others for the proteinase from rat liver but resembles the structure of the simpler archaebacterial proteasome. The possibility of conformational changes associated with the addition of effectors of proteolytic activity has been investigated by sedimentation velocity analysis and dynamic light-scattering measurement...
Proteasomes and other self-compartmentalizing proteases in prokaryotes
Trends in Microbiology, 1999
I ntracellular proteases in prokaryotic cells perform many tasks, including cleavage of signal peptides during protein export, timely inactivation of regulatory proteins, and removal of aberrant nonfunctional proteins 1. Obviously, proteolysis inside prokaryotic cells needs to be controlled to avoid unwanted degradation. Spatial safeguarding can be provided by directing a protease to a specific compartment of the cell, such as the periplasmic space of Gram-negative bacteria. Autocompartmentalization, as a common strategy to curtail the potential hazard associated with intracellular protein breakdown, has recently emerged from the elucidation of the structure of a subset of cytoplasmic proteases in prokaryotes 2. Isolation of proteolytic activity is achieved by self-assembly of proteolytic subunits into a cylinder-shaped complex, in which the active sites are confined to nanocompart-ments in their interior (Fig. 1). Narrow entrances to the cylinder restrict access to unfolded proteins. The ATPase complexes that can bind to both ends of such barrels are thought to be involved in the initial binding, unfolding and translocation of substrates. Proteases creating nanocompartments The proteasome, which has become the paradigm of a selfcompartmentalizing protease 3 , was first discovered in eukaryotic cells, where it constitutes the major non-lysosomal proteolytic system 4. The proteolytic core (20S proteasome), capped with 19S regulatory complexes (including several ATPases), is designated the 26S proteasome and mediates the ATP-dependent degradation of ubiquitin-bound proteins 5. The archaeal counterpart of the 20S proteasome was identified in Thermoplasma acidophilum about a decade ago 6. The discovery of The proteasome represents the major nonlysosomal proteolytic system in eukaryotes. It confines proteolytic activity to an inner compartment that is accessible to unfolded proteins only. The strategy of controlling intracellular breakdown of proteins by self-compartmentalization is also used by different types of prokaryotic energy-dependent proteases. Genomic sequencing data reveal that various combinations of these energy-dependent proteases occur in prokaryotic cells from different lineages.
Proteasome: from structure to function
Current Opinion in Biotechnology, 1996
During the past two years, significant progress has been made in understanding the structure and function of the proteasome. Recent work has revealed the three-dimensional structure of the 700 kDa proteolytic complex at atomic resolution and elucidated its novel catalytic mechanism. Close relationships to a number of other amino-terminal hydrolases have emerged, making the proteasomal subunits the prototype of this newly discovered structural superfamily.
Journal of Biological Chemistry, 1988
Latent multicatalytic protease complexes, named proteasomes, were purified to apparent homogeneity from various eukaryotic sources, such as human, rat, and chicken liver, Xenopus laevis ovary, and yeast (Saccharomyces cerevisiae), and their functional and structural properties were compared. They showed latency in breakdown of [methyLSH]casein, but were greatly activated in various ways, such as by addition of polylysine. They all degraded three types of fluorogenic oligopeptides at the carboxyl side of basic, neutral, and acidic amino acids, and the three cleavage reactions showed different spectra for inhibition, suggesting that they had three distinct active sites. The proteasomes all seemed to be seryl endopeptidases with similar pH optima in the weakly alkaline region. Their physicochemical properties, such as their sedimentation coefficients (19 S to 22 S) , diffusion coefficients (2.0-2.6 X lo-' cm2 s-'), molecular masses (700-900