Molecular Chaperone Functions of Heat-Shock Proteins

Hendrick, Joseph P.; Hartl, F. Ulrich

doi:10.1146/annurev.bi.62.070193.002025

Cited by 1,533 publications

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“…Hsp70 is a molecular chaperone required for posttranslational protein translocation that prevents premature protein folding (Brodsky, 1996;Hendrick and Hartl, 1993). Interestingly, the RLD-2 domain of p532 that interacts with clathrin also mediates the interaction with ARF1 (Rosa et al, 1996a) suggesting that clathrin, together with Hsp70, may chaperone cytosolic p532.…”

Section: Discussionmentioning

confidence: 99%

A giant protein that stimulates guanine nucleotide exchange on ARF1 and Rab proteins forms a cytosolic ternary complex with clathrin and Hsp70

Rosa

Barbacid

1997

Oncogene

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We have recently identi®ed an unusually large human protein that stimulates guanine nucleotide exchange on ARF1 and Rab proteins (EMBO J 15: 4262 ± 4273, 1996). This protein, designated p532 based on its predicted molecular weight (EMBO J 15: 5738, 1996), contains multiple structural domains including two regions of seven internal repeats highly related to the cell cycle regulator RCC1, a guanine nucleotide exchange factor for the small GTP-binding protein Ran, seven b-repeat domains characteristic of the b subunit of heterotrimeric G proteins, three putative SH3 binding sites, a putative leucine-zipper and a carboxyterminal HECT domain characteristic of E3 ubiquitinprotein ligases. Some of these domains are known to be involved in protein-protein interactions, suggesting the existence of p532-interacting proteins. To identify some of these proteins, we used the carboxy-terminal RCC1-like domain (RLD) of p532 in the yeast two-hybrid system. We report here the isolation of a clone that encodes the last 654 amino acid residues of the clathrin heavy chain. This interaction involves amino acid residues 1315 ± 1557 of the clathrin heavy chain and the carboxy, but not the amino-terminal RLD of p532. p532 has been located in the cytosolic fraction as well as in the Golgi apparatus. The interaction between p532 and clathrin only occurs in the cytosol and is mediated by the formation of an ATP-dependent ternary complex with the heat shock protein, Hsp70. These observations suggest that p532 is involved in membrane transport processes.

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Section: Discussionmentioning

confidence: 99%

A giant protein that stimulates guanine nucleotide exchange on ARF1 and Rab proteins forms a cytosolic ternary complex with clathrin and Hsp70

Rosa

Barbacid

1997

Oncogene

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“…Both GroEL and GroES have been extensively studied [3][4][5][6][7][8][9][10][11][12][13] and are found involved in assisting the folding of other proteins both in vivo and in vitro [14][15][16][17]. Each monomer of GroES has a nominal molecular weight of 10 kDa [2], and the GroES is normally found in an oligomeric configuration of seven subunits [2,13].…”

Section: Introductionmentioning

confidence: 99%

“…Although no specific functions have been identified with the GroES heptamer alone, it has been firmly established with both electron microscopy (EM) and biochemical methods that, in the presence of ATP or ADP, the GroES heptamer can form a stable complex with the GroEL tetradecamer [5,8,[18][19][20]. Upon the binding of GroES, the rate of ATP hydrolysis of GroEL is strongly affected [4,6,7,9,12,21], but the mechanism has not been well understood [14][15][16][17]. However, it is convincingly demonstrated that the folding of non-native state proteins by GroEL requires the participation of GroES and ATP under 'non-permissive' conditions, under which spontaneous folding could not occur [9,21,22].…”

Section: Introductionmentioning

confidence: 99%

High resolution surface structure of E. coli GroES oligomer by atomic force microscopy

et al. 1996

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Using atomic force microscopy (AFM) in aqueous solution, we show that the surface structure of the oligomeric GroES can be obtained up to 10 A resolution. The seven subunits of the heptamer were well resolved without image averaging. The overall dimension of the GroES heptamer was 8.4+0.4 nm in diameter and 3.0+0.3 nm high. However, the AFM images further suggest that there is a central protrusion of 0.8+0.2 nm high and 4.5+0.4 nm in diameter on one side of GroES which displays a profound seven-fold symmetry. It was found that GroEL could not bind to the adsorbed GroES in the presence of AMP-PNP and Mg 2+, suggesting that the side of GroES with the central protrusion faces away from the GroEL lumen, because only one side of GroES was observed under these conditions. Based on the results from both electron and atomic force microscopy, a surface model for the GroES is proposed.Key words: Atomic force microscopy; GroES; GroEL; Resolution subunits were not discernible [18]. Because of the variable conformations observed by EM, it was even suggested that GroES could have a flexible structure or a symmetry other than the seven-fold [18]. Since the atomic force microscopy (AFM) has been shown to be capable of obtaining high resolution surface structures of several oligomeric bacterial proteins (for recent reviews, see [24][25][26]), we have applied this method to determine the surface structure of GroES under aqueous solutions. We show that the subunit structure can be clearly resolved in the AFM images without image processing/averaging. Surface structures beyond the subunits were also resolved, demonstrating a surface resolution of 10 A or so, which is much higher than that from EM images. In combination with the results from EM, a model for the GroES is also proposed. Materials and methods

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“…A regulated, ATP-dependent association-dissociation cycle of the complex ensures the correct fate of the protein in vivo, which may be proper folding after synthesis, assembly into a multimeric complex, or translocation across a variety of intracellular membranes (5)(6)(7)(8). Some of the chaperones are induced by stress, such as heat (heat shock proteins), and are probably involved in refolding of stress-induced denatured proteins.…”

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confidence: 99%

Ubiquitin-dependent Degradation of Certain Protein Substrates in Vitro Requires the Molecular Chaperone Hsc70

Bercovich

Stancovski

Mayer

et al. 1997

Journal of Biological Chemistry

274

177

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Degradation of a protein via the ubiquitin system involves two discrete steps, signaling by covalent conjugation of multiple moieties of ubiquitin and degradation of the tagged substrate. Conjugation is catalyzed via a three-step mechanism that involves three distinct enzymes that act successively: E1, E2, and E3. The first two enzymes catalyze activation of ubiquitin and transfer of the activated moiety to E3, respectively. E3, to which the substrate is specifically bound, catalyzes formation of a polyubiquitin chain that is anchored to the targeted protein. The polyubiquitin-tagged protein is degraded by the 26 S proteasome, and free and reutilizable ubiquitin is released. In addition to the three conjugating enzymes, targeting of certain proteins requires association with ancillary proteins and/or post-translational modification(s). Using a specific antibody to deplete cell extract from the molecular chaperone Hsc70, we demonstrate that this protein is required for the degradation of actin, ␣-crystallin, glyceraldehyde-3-phosphate dehydrogenase, ␣-lactalbumin, and histone H2A. In contrast, the degradation of bovine serum albumin, lysozyme, and oxidized RNase A is Hsc70-independent. Mechanistic analysis revealed that the chaperone is required for the conjugation reaction; however, it does not substitute for E3. Involvement of the chaperone in the proteolytic process requires complex formation with the substrate. Formation of this complex appears to be essential in the proteolytic process. In addition, the proper function of the chaperone in the proteolytic process requires the presence of K ؉ , which allows rapid cycles of dissociation and association of the complex. The chaperone may act by binding to the substrate and unfolding it to expose a ubiquitin ligase-binding site. In addition, it can also act directly on the ubiquitination machinery.Degradation of short-lived and key regulatory proteins via the ubiquitin-proteasome pathway plays important roles in basic cellular processes. Protein targets of the ubiquitin system include, among others, cyclins, cyclin-dependent kinases and their inhibitors, tumor suppressors, oncoproteins, and transcriptional activators and their inhibitors. Selection of proteins for degradation can be mediated via primary (constitutive) or secondary signals such as post-translational modifications or via association with ancillary proteins. These signals are recognized by specific ubiquitin-protein ligases (E3), 1 to which the substrate proteins bind prior to ubiquitination. Thus, the ligases play a key role in the ubiquitin proteolytic cascade, recognition and selection of proteins for conjugation and subsequent degradation. Following formation of the polyubiquitin adduct, the protein moiety is degraded by the 26 S proteasome complex, and free and reutilizable ubiquitin is released (reviewed in Refs. 1-4).Molecular chaperones comprise a set of universally conserved proteins that bind and stabilize conformers of other proteins. A regulated, ATP-dependent association-dissociation cyc...

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Molecular Chaperone Functions of Heat-Shock Proteins

Cited by 1,533 publications

References 0 publications

A giant protein that stimulates guanine nucleotide exchange on ARF1 and Rab proteins forms a cytosolic ternary complex with clathrin and Hsp70

A giant protein that stimulates guanine nucleotide exchange on ARF1 and Rab proteins forms a cytosolic ternary complex with clathrin and Hsp70

High resolution surface structure of E. coli GroES oligomer by atomic force microscopy

Ubiquitin-dependent Degradation of Certain Protein Substrates in Vitro Requires the Molecular Chaperone Hsc70

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