Localization of a sequence motif complementary to the nuclear localization signal in proteasomes from Thermoplasma acidophilum by immunoelectron microscopy

Grziwa, Anja; Dahlmann, Burkhardt; Cejka, Zdenka; Santarius, Ute; Baumeister, Wolfgang

doi:10.1016/1047-8477(92)90048-f

Cited by 15 publications

(10 citation statements)

References 33 publications

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“…1D) (3,14,41,45,62,74). Based on analogy to the T. acidophilum 20S proteasome (25), it is likely that the ␣ protein of M. jannaschii forms the outer protein rings of the cylinder as well as the distinct central openings. If so, assembly of the ␣ disc-like complexes with the ␤(⌬pro) protein may involve conformational changes in ␣ which generate the central portal and 2-nm increase in diameter of the 20S proteasome ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Biochemical and Physical Properties of theMethanococcus jannaschii20S Proteasome and PAN, a Homolog of the ATPase (Rpt) Subunits of the Eucaryal 26S Proteasome

Wilson

Aldrich

et al. 2000

J Bacteriol

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The 20S proteasome is a self-compartmentalized protease which degrades unfolded polypeptides and has been purified from eucaryotes, gram-positive actinomycetes, and archaea. Energy-dependent complexes, such as the 19S cap of the eucaryal 26S proteasome, are assumed to be responsible for the recognition and/or unfolding of substrate proteins which are then translocated into the central chamber of the 20S proteasome and hydrolyzed to polypeptide products of 3 to 30 residues. All archaeal genomes which have been sequenced are predicted to encode proteins with up to ϳ50% identity to the six ATPase subunits of the 19S cap. In this study, one of these archaeal homologs which has been named PAN for proteasome-activating nucleotidase was characterized from the hyperthermophile Methanococcus jannaschii. In addition, the M. jannaschii 20S proteasome was purified as a 700-kDa complex by in vitro assembly of the ␣ and ␤ subunits and has an unusually high rate of peptide and unfolded-polypeptide hydrolysis at 100°C. The 550-kDa PAN complex was required for CTP-or ATP-dependent degradation of ␤-casein by archaeal 20S proteasomes. A 500-kDa complex of PAN(⌬1-73), which has a deletion of residues 1 to 73 of the deduced protein and disrupts the predicted N-terminal coiled-coil, also facilitated this energy-dependent proteolysis. However, this deletion increased the types of nucleotides hydrolyzed to include not only ATP and CTP but also ITP, GTP, TTP, and UTP. The temperature optimum for nucleotide ( Energy-dependent proteolysis is not only vital to elimination of defective cellular proteins but is also central to regulation of cell division, metabolism, transcription, and other essential cellular functions (12,22). A small group of related energydependent proteases have been identified from several diverse organisms; these proteases include Lon, FtsH (HflB), ClpAP, ClpXP, HslUV (ClpYQ), and the 26S proteasome (4, 39). Although this group of proteins shares limited primary sequence identity, the proteases have converged to a universal structure in which relatively nonspecific proteolytic active sites are compartmentalized from the cell by narrow openings (37, 67). The current model is that the degradation of biological substrates by this group of proteases requires additional energy-dependent proteins or protein domains for the recognition and/or unfolding of substrate proteins (21,29,65). Some of these energy-dependent components may not only participate in proteolysis but also have independent roles as chaperones (60). Thus, the energy-dependent component of these proteases may provide a proofreading step following the initial binding of protein substrates and enable the cell to distinguish between proteins destined for refolding, disaggregation, or destruction (23).Some energy-dependent proteases are organized in a symmetry mismatch, including ClpAP and ClpXP which are complexes of the hexameric ClpA and ClpX ATPases interfaced with the ClpP protease of two heptameric rings (5). It is postulated that hydrolysis of nucleotides...

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Section: Resultsmentioning

confidence: 99%

Biochemical and Physical Properties of theMethanococcus jannaschii20S Proteasome and PAN, a Homolog of the ATPase (Rpt) Subunits of the Eucaryal 26S Proteasome

Wilson

Aldrich

et al. 2000

J Bacteriol

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“…However, current data cannot exclude the possibility that only doubly capped proteasomes are activated. These data also indicate that the two terminal rings of the proteasome are structurally and functionally equivalent (or identical), a model supported by strong data from studies of both eukaryotic and archaebacterial proteasomes [19,20],…”

Section: Pa 2 8 Forms a Complex With The Proteasomementioning

confidence: 49%

Regulatory Proteins of the Proteasome

DeMartino

Slaughter

1993

Enzyme Protein

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The function of the proteasome is controlled by a variety of specific regulatory proteins including activators, inhibitors, and modulators. Two recently discovered activators, termed PA28 and PA700, bind to the terminal rings of the proteasome to form proteasome-regulator complexes which display greatly increased proteolytic activity. PA28 is a high-affinity activator of the proteasome’s multiple peptidase activities. The carboxyl terminus of PA28 is required for its binding to the proteasome. PA700 binds to the proteasome via an ATP-dependent mechanism. PA700 has ATPase activity, and at least four of PA700’s 16 subunits are members of a protein family containing a concensus sequence for ATP binding. Proteasome- PA700 complexes are activated with respect to both the hydrolysis of peptide substrates and the hydrolysis of ubiquitinated proteins.

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“…The ␣ proteins form the outer rings (18) and are required for the ␤ proteins to be processed during formation of inner rings which harbor the active-site N-terminal threonine (13,25,26,31,38). The number of subunits forming 20S proteasomes varies.…”

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confidence: 99%

Subunit Topology of Two 20S Proteasomes from Haloferax volcanii

Kaczowka

Maupin-Furlow

2003

J Bacteriol

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Haloferax volcanii, a halophilic archaeon, synthesizes three different proteins (␣1, ␣2, and ␤) which are classified in the 20S proteasome superfamily. The ␣1 and ␤ proteins alone form active 20S proteasomes; the role of ␣2, however, is not clear. To address this, ␣2 was synthesized with an epitope tag and purified by affinity chromatography from recombinant H. volcanii. The ␣2 protein copurified with ␣1 and ␤ in a complex with an overall structure and peptide-hydrolyzing activity comparable to those of the previously described ␣1-␤ proteasome. Supplementing buffers with 10 mM CaCl 2 stabilized the halophilic proteasomes in the absence of salt and enabled them to be separated by native gel electrophoresis. This facilitated the discovery that wild-type H. volcanii synthesizes more than one type of 20S proteasome. Two 20S proteasomes, the ␣1-␤ and ␣1-␣2-␤ proteasomes, were identified during stationary phase. Cross-linking of these enzymes, coupled with available structural information, suggested that the ␣1-␤ proteasome was a symmetrical cylinder with ␣1 rings on each end. In contrast, the ␣1-␣2-␤ proteasome appeared to be asymmetrical with homo-oligomeric ␣1 and ␣2 rings positioned on separate ends. Inter-␣-subunit contacts were only detected when the ratio of ␣1 to ␣2 was perturbed in the cell using recombinant technology. These results support a model that the ratio of ␣ proteins may modulate the composition and subunit topology of 20S proteasomes in the cell.Proteasomes are large, energy-dependent proteases. These enzyme structures form nanocompartments within the cell (2, 27) that degrade proteins into oligopeptides of 3 to 30 amino acids in length by processive hydrolysis (1, 24). The catalytic core responsible for this proteolytic activity is a 20S particle, universally distributed among the Archaea, Eucarya, and grampositive actinomycetes (10, 12). The 20S proteasome particle (11 to 12 nm in diameter and 15 nm in length) is a cylindrical bundle of four-stacked, heptameric rings. This barrel-shaped structure includes a central channel with narrow (1.3 nm) openings on each end which limits substrate access (32). Each opening is connected to a central chamber responsible for the hydrolysis of peptide bonds (20,21,25). "Unfoldases" such as the eucaryal 19S cap and archaeal PAN protein associate with 20S proteasomes and stimulate the energy-dependent degradation of proteins (17,34,37,39).The subunits that form 20S proteasomes have been classified into two related superfamilies (␣ and ␤) (9). The ␣ proteins form the outer rings (18) and are required for the ␤ proteins to be processed during formation of inner rings which harbor the active-site N-terminal threonine (13,25,26,31,38). The number of subunits forming 20S proteasomes varies. Many lower eucaryotes such as yeast produce a single symmetrical 20S proteasome of 14 different subunits (i.e., two copies each of ␣1 to ␣7 and ␤1 to ␤7) (20). Higher eucaryotes express additional subunits (e.g., ␤1i, ␤2i, ␤5i) that form auxiliary 20S proteasomes (e.g., the immuno...

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Localization of a sequence motif complementary to the nuclear localization signal in proteasomes from Thermoplasma acidophilum by immunoelectron microscopy

Cited by 15 publications

References 33 publications

Biochemical and Physical Properties of theMethanococcus jannaschii20S Proteasome and PAN, a Homolog of the ATPase (Rpt) Subunits of the Eucaryal 26S Proteasome

Biochemical and Physical Properties of theMethanococcus jannaschii20S Proteasome and PAN, a Homolog of the ATPase (Rpt) Subunits of the Eucaryal 26S Proteasome

Regulatory Proteins of the Proteasome

Subunit Topology of Two 20S Proteasomes from Haloferax volcanii

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