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A novel function of 14-3-3 protein: 14-3-3zeta is a heat-shock-related molecular chaperone that dissolves thermal-aggregated proteins.

ABSTRACT: The 14-3-3 proteins are highly conserved molecules that function as intracellular adaptors in a variety of biological processes, such as signal transduction, cell cycle control, and apoptosis. Here, we show that a 14-3-3 protein is a heat-shock protein (Hsp) that protects cells against physiological stress as its new cellular function. We have observed that, in Drosophila cells, the 14-3-3zeta is up-regulated under heat stress conditions, a process mediated by a heat shock transcription factor. As the biological action linked to heat stress, 14-3-3zeta interacted with apocytochrome c, a mitochondrial precursor protein of cytochrome c, in heat-treated cells, and the suppression of 14-3-3zeta expression by RNA interference resulted in the formation of significant amounts of aggregated apocytochrome c in the cytosol. The aggregated apocytochrome c was converted to a soluble form by the addition of 14-3-3zeta protein and ATP in vitro. 14-3-3zeta also resolubilized heat-aggregated citrate synthase and facilitated its reactivation in cooperation with Hsp70/Hsp40 in vitro. Our observations provide the first direct evidence that a 14-3-3 protein functions as a stress-induced molecular chaperone that dissolves and renaturalizes thermal-aggregated proteins.

SUBMITTER: Yano M

PROVIDER: S-EPMC1635386 | biostudies-literature | 2006 Nov

REPOSITORIES: biostudies-literature

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A novel function of 14-3-3 protein: 14-3-3zeta is a heat-shock-related molecular chaperone that dissolves thermal-aggregated proteins.

Yano Mihiro M Nakamuta Shinichi S Wu Xueji X Okumura Yuushi Y Kido Hiroshi H

Molecular biology of the cell 20060830 11

The 14-3-3 proteins are highly conserved molecules that function as intracellular adaptors in a variety of biological processes, such as signal transduction, cell cycle control, and apoptosis. Here, we show that a 14-3-3 protein is a heat-shock protein (Hsp) that protects cells against physiological stress as its new cellular function. We have observed that, in Drosophila cells, the 14-3-3zeta is up-regulated under heat stress conditions, a process mediated by a heat shock transcription factor. ...[more]

PMID: 16943323

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Project description:Small heat shock proteins (sHsps) are a ubiquitous part of the machinery that maintains cellular protein homeostasis by acting as molecular chaperones. sHsps bind to and prevent the aggregation of partially folded substrate proteins in an ATP-independent manner. sHsps are dynamic, forming an ensemble of structures from dimers to large oligomers through concentration-dependent equilibrium dissociation. Based on structural studies and mutagenesis experiments, it is proposed that the dimer is the smallest active chaperone unit, while larger oligomers may act as storage depots for sHsps or play additional roles in chaperone function. The complexity and dynamic nature of their structural organization has made elucidation of their chaperone function challenging. HspB1 and HspB5 are two canonical human sHsps that vary in sequence and are expressed in a wide variety of tissues. In order to determine the role of the dimer in chaperone activity, glutathione-S-transferase (GST) was genetically linked as a fusion protein to the N-terminus regions of both HspB1 and HspB5 (also known as Hsp27 and αB-crystallin, respectively) proteins in order to constrain oligomer formation of HspB1 and HspB5, by using GST, since it readily forms a dimeric structure. We monitored the chaperone activity of these fusion proteins, which suggest they primarily form dimers and monomers and function as active molecular chaperones. Furthermore, the two different fusion proteins exhibit different chaperone activity for two model substrate proteins, citrate synthase (CS) and malate dehydrogenase (MDH). GST-HspB1 prevents more aggregation of MDH compared to GST-HspB5 and wild type HspB1. However, when CS is the substrate, both GST-HspB1 and GST-HspB5 are equally effective chaperones. Furthermore, wild type proteins do not display equal activity toward the substrates, suggesting that each sHsp exhibits different substrate specificity. Thus, substrate specificity, as described here for full-length GST fusion proteins with MDH and CS, is modulated by both sHsp oligomeric conformation and by variations of sHsp sequences.

Project description:BACKGROUND: A small heat shock protein AgsA was originally isolated from Salmonella enterica serovar Typhimurium. We previously demonstrated that AgsA was an effective chaperone that could reduce the amount of heat-aggregated proteins in an Escherichia coli rpoH mutant. AgsA appeared to promote survival at lethal temperatures by cooperating with other chaperones in vivo. To investigate the aggregation prevention mechanisms of AgsA, we constructed N- or C-terminal truncated mutants and compared their properties with wild type AgsA. RESULTS: AgsA showed significant overall homology to wheat sHsp16.9 allowing its three-dimensional structure to be predicted. Truncations of AgsA until the N-terminal 23rd and C-terminal 11th amino acid (AA) from both termini preserved its in vivo chaperone activity. Temperature-controlled gel filtration chromatography showed that purified AgsA could maintain large oligomeric complexes up to 50 degrees C. Destabilization of oligomeric complexes was observed for N-terminal 11- and 17-AA truncated AgsA; C-terminal 11-AA truncated AgsA could not form large oligomeric complexes. AgsA prevented the aggregation of denatured lysozyme, malate dehydrogenase (MDH) and citrate synthase (CS) but did not prevent the aggregation of insulin at 25 degrees C. N-terminal 17-AA truncated AgsA showed no chaperone activity towards MDH. C-terminal 11-AA truncated AgsA showed weak or no chaperone activity towards lysozyme, MDH and CS although it prevented the aggregation of insulin at 25 degrees C. When the same amount of AgsA and C-terminal 11-AA truncated AgsA were mixed (half of respective amount required for efficient chaperone activities), good chaperone activity for all substrates and temperatures was observed. Detectable intermolecular exchanges between AgsA oligomers at 25 degrees C were not observed using fluorescence resonance energy transfer analysis; however, significant exchanges between AgsA oligomers and C-terminal truncated AgsA were observed at 25 degrees C. CONCLUSIONS: Our data demonstrate that AgsA has several regions necessary for efficient chaperone activity: region(s) important for lysozyme chaperone activity are located outer surface of the oligomeric complex while those region(s) important for insulin are located inside the oligomeric complex and those for MDH are located within the N-terminal arm. In addition, the equilibrium between the oligomer and the dimer structures appears to be important for its efficient chaperone activity.

Dataset Information

A novel function of 14-3-3 protein: 14-3-3zeta is a heat-shock-related molecular chaperone that dissolves thermal-aggregated proteins.

Publications

A novel function of 14-3-3 protein: 14-3-3zeta is a heat-shock-related molecular chaperone that dissolves thermal-aggregated proteins.

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