Conformational constraints for protein self-cleavage in the proteasome1 (original) (raw)
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Conformational constraints for protein self-cleavage in the proteasome
Journal of Molecular Biology, 1998
The proteasome is the central enzyme of protein degradation in the cytosol and the nucleus. It is involved in the removal of abnormal, misfolded or incorrectly assembled proteins, in the processing or degradation of transcriptional regulators in stress response, in degradation of cyclins in cell-cycle control, in the destruction of transcription factors or metabolic enzymes in cell differentiation and metabolic response, and in MHC class I mediated cellular immune response. By the analysis of the crystal and molecular structures of the 20 S proteasomes from the archaeon Thermoplasma acidophilum and from yeast it was shown that the b-type subunits in which the proteolytic activities reside are members of the N-terminal nucleophile (Ntn) protein family. They are synthesized as proproteins and become active by autoprocessing at a Gly À 1 ±Thr1 bond.
Catalytic Mechanism and Assembly of the Proteasome
Chemical Reviews, 2009
Figure 5. Localization and structure of substrate binding S1 pockets of the yeast proteasome. (A) S. cereVisiae 20S proteasome shown in a surface representation with a cut open view of the catalytic chamber. (B) Magnification of the 1 subunit showing the localization of the active residues in a cleft. (C) Shown are the S1 pockets of the three active site subunits. The pocket forming residues are indicated. In (A-C), the three main residues (Thr1, Asp17, and Lys33) are shown in red. The figure was prepared using PyMOL.
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.
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...
Molecular Architecture and Assembly of the Eukaryotic Proteasome
Annual Review of Biochemistry, 2013
The eukaryotic ubiquitin-proteasome system is responsible for most cellular quality-control and regulatory protein degradation. Its substrates, which are usually modified by polymers of ubiquitin, are ultimately degraded by the 26S proteasome. This 2.6 MDa protein complex is separated into a barrel-shaped proteolytic 20S core particle (CP) of 28 subunits capped on one or both ends by a 19S regulatory particle (RP) comprising at least 19 subunits. The RP coordinates substrate recognition, removal of substrate polyubiquitin chains, and substrate unfolding and translocation into the CP for degradation. While many atomic structures of the CP have been determined, the RP has resisted high-resolution analysis. Recently, however, a combination of cryo-electron microscopy (cryo-EM), biochemical analysis, and crystal structure determination of several RP subunits has yielded a near-atomic resolution view of much of the complex. Major new insights into chaperone-assisted proteasome assembly have also recently been made. Here we review these novel findings.
Structure and structure formation of the 20S proteasome
Molecular biology reports, 1997
Eukaryotic 20S proteasomes are complex oligomeric proteins. The maturation process of the 14 different alpha- and beta-subunits has to occur in a highly coordinate manner. In addition beta-subunits are synthesized as proproteins and correct processing has to be guaranteed during complex maturation. The structure formation can be subdivided in different phases. The knowledge of the individual phases is summarized in this publication. As a first step the newly synthesized monomers have to adopt the correct tertiary structure, a process that might be supported in the case of the beta-subunits by the intramolecular chaperone activity postulated for the prosequences. Subsequently the alpha-subunits form ring-like structures thereby providing docking sites for the different beta-subunits. The result most likely is a double ring structure (13S precursor) representing half-proteasomes, which contain immature proproteins. Two 13S precursors associate to form the proteolytically inactive 16S ...
Proceedings of the National Academy of Sciences, 1999
We present a biochemical and crystallographic characterization of active site mutants of the yeast 20S proteasome with the aim to characterize substrate cleavage specificity, subunit intermediate processing, and maturation. 1(Pre3), 2(Pup1), and 5(Pre2) are responsible for the postacidic, tryptic, and chymotryptic activity, respectively. The maturation of active subunits is independent of the presence of other active subunits and occurs by intrasubunit autolysis. The propeptides of 6(Pre7) and 7(Pre4) are intermediately processed to their final forms by 2(Pup1) in the wild-type enzyme and by 5(Pre2) and 1(Pre3) in the 2(Pup1) inactive mutants. A role of the propeptide of 1(Pre3) is to prevent acetylation and thereby inactivation. A gallery of proteasome mutants that contain active site residues in the context of the inactive subunits 3(Pup3), 6(Pre7), and 7(Pre4) show that the presence of Gly-1, Thr1, Asp17, Lys33, Ser129, Asp166, and Ser169 is not sufficient to generate activity.