Gymnastics of Molecular Chaperones

Cytosolic Hsp60 can modulate proteasome activity in yeast

Hsp60, an essential oligomeric molecular mitochondrial chaperone, has been subject to rigorous basic and clinical research. With yeast as a model system, we provide evidence for the ability of cytosolic yHsp60 to inhibit the yeast proteasome. (i) Following biological turnover of murine Bax (a proteasome substrate), we show that co-expression of cytosolic yHsp60 stabilizes Bax, enhances its association with mitochondria, and enhances its killing capacity. (ii) Expression of yHsp60 in the yeast cytosol (yHsp60c) inhibits degradation of a cytosolic protein ΔMTS-Aco1 tagged with the degron SL17 (a ubiquitin-proteasome substrate). (iii) Conditions under which Hsp60 accumulates in the cytosol (elevated Hsp60c or growth at 37 °C) correlate with reduced 20 S peptidase activity in proteasomes purified from cell extracts. (iv) Elevated yHsp60 in the cytosol correlate with accumulation of polyubiquitinated proteins. (v) According to 20 S proteasome pulldown experiments, Hsp60 is physically associated with proteasomes in extracts of cells expressing Hsp60c or grown at 37 °C. Even mutant Hsp60 proteins, lacking chaperone activity, were still capable of proteasome inhibition. The results support the hypothesis that localization of Hsp60 to the cytosol may modulate proteasome activity according to cell need.

Protein chaperones: a composition of matter review (2008 - 2013)

INTRODUCTION

Heat shock proteins (Hsps) are proteins with important functions in regulating disease phenotypes. Historically, Hsp90 has first received recognition as a target in cancer, with consequent efforts extending its potential role to other diseases. Hsp70 has also attracted interest as a therapeutic target for its role as a co-chaperone to Hsp90 as well as its own anti-apoptotic roles.

AREAS COVERED

Herein, patents from 2008 to 2013 are reviewed to identify those that disclose composition of matter claimed to inhibit Hsp90 or Hsp70.

EXPERT OPINION

For Hsp90, there has been considerable creativity in the discovery of novel pharmacophores that fall outside the three initially discovered scaffolds (i.e., ansamycins, resorcinols and purines). Nonetheless, much of the patent literature appears to build on previously reported structure activity relationship through slight modifications of Hsp90 inhibitor space by finding weaknesses in existing patents. The major goal of future development of Hsp90 inhibitors is not necessarily identifying better molecules but rather understanding how to rationally use these agents in the clinic. The development of Hsp70 inhibitors has lagged behind. It will require a more concerted effort from the drug discovery community in order to begin to realize the potential of this target.

Regulation of protein turnover by heat shock proteins

Protein turnover reflects the balance between synthesis and degradation of proteins, and it is a crucial process for the maintenance of the cellular protein pool. The folding of proteins, refolding of misfolded proteins, and also degradation of misfolded and damaged proteins are involved in the protein quality control (PQC) system. Correct protein folding and degradation are controlled by many different factors, one of the most important of which is the heat shock protein family. Heat shock proteins (HSPs) are in the class of molecular chaperones, which may prevent the inappropriate interaction of proteins and induce correct folding. On the other hand, these proteins play significant roles in the degradation pathways, including endoplasmic reticulum-associated degradation (ERAD), the ubiquitin-proteasome system, and autophagy. This review focuses on the emerging role of HSPs in the regulation of protein turnover; the effects of HSPs on the degradation machineries ERAD, autophagy, and proteasome; as well as the role of posttranslational modifications in the PQC system.

Relationship between HSP70-2 A+1267G Polymorphism and Cardiovascular Events of Chinese Peritoneal Dialysis Patients

BACKGROUND

Heat shock proteins (HSPs) are expressed by cells in response to various environmental stresses. A single-nucleotide polymorphism A+1267G of the HSPA1B gene affects the expression of HSP70-2, with the A allele being protective against inflammatory conditions. We investigated the relation between the HSP A+1267G polymorphism and the clinical outcomes of Chinese peritoneal dialysis (PD) patients.

METHODS

We studied 347 new PD cases (181 males, age 56.6 ± 13.7 years). Genotyping was done by standard methods. Patients were followed for 40.5 ± 20.7 months for survival analysis.

RESULTS

For the entire cohort, there was no difference in the 5-year survival between genotype groups. However, there was a significant interaction between HSP polymorphism and diabetic status on the cardiovascular event-free survival. In patients without pre-existing diabetes, 5-year cardiovascular event-free survival of the GG/AG genotype group was significantly better than that of the AA genotype group (57.2 vs. 32.1%, p = 0.011).

CONCLUSION

The G allele of the HSP70-2 A+1267G polymorphism confers survival advantages in non-diabetic PD patients. The role of HSP in the pathogenesis of cardiovascular disease in renal failure patients needs further investigation.

Single-molecule spectroscopy reveals chaperone-mediated expansion of substrate protein

Molecular chaperones are an essential part of the machinery that avoids protein aggregation and misfolding in vivo. However, understanding the molecular basis of how chaperones prevent such undesirable interactions requires the conformational changes within substrate proteins to be probed during chaperone action. Here we use single-molecule fluorescence spectroscopy to investigate how the DnaJ-DnaK chaperone system alters the conformational distribution of the denatured substrate protein rhodanese. We find that in a first step the ATP-independent binding of DnaJ to denatured rhodanese results in a compact denatured ensemble of the substrate protein. The following ATP-dependent binding of multiple DnaK molecules, however, leads to a surprisingly large expansion of denatured rhodanese. Molecular simulations indicate that hard-core repulsion between the multiple DnaK molecules provides the underlying mechanism for disrupting even strong interactions within the substrate protein and preparing it for processing by downstream chaperone systems.

Tombusvirus-yeast interactions identify conserved cell-intrinsic viral restriction factors

To combat viral infections, plants possess innate and adaptive immune pathways, such as RNA silencing, R gene and recessive gene-mediated resistance mechanisms. However, it is likely that additional cell-intrinsic restriction factors (CIRF) are also involved in limiting plant virus replication. This review discusses novel CIRFs with antiviral functions, many of them RNA-binding proteins or affecting the RNA binding activities of viral replication proteins. The CIRFs against tombusviruses have been identified in yeast (Saccharomyces cerevisiae), which is developed as an advanced model organism. Grouping of the identified CIRFs based on their known cellular functions and subcellular localization in yeast reveals that TBSV replication is limited by a wide variety of host gene functions. Yeast proteins with the highest connectivity in the network map include the well-characterized Xrn1p 5'-3' exoribonuclease, Act1p actin protein and Cse4p centromere protein. The protein network map also reveals an important interplay between the pro-viral Hsp70 cellular chaperone and the antiviral co-chaperones, and possibly key roles for the ribosomal or ribosome-associated factors. We discuss the antiviral functions of selected CIRFs, such as the RNA binding nucleolin, ribonucleases, WW-domain proteins, single- and multi-domain cyclophilins, TPR-domain co-chaperones and cellular ion pumps. These restriction factors frequently target the RNA-binding region in the viral replication proteins, thus interfering with the recruitment of the viral RNA for replication and the assembly of the membrane-bound viral replicase. Although many of the characterized CIRFs act directly against TBSV, we propose that the TPR-domain co-chaperones function as "guardians" of the cellular Hsp70 chaperone system, which is subverted efficiently by TBSV for viral replicase assembly in the absence of the TPR-domain co-chaperones.

The susceptibility of corals to thermal stress by analyzing Hsp60 expression

Due to the increasing frequency and severity of the coral bleaching events in the context of global warming, there is an urgent need to improve our understanding of the susceptibility of corals to thermal stresses, particularly at the sub-cellular level. In this context, we examined the modulation of the polyp mitochondrial Hsp60 in three scleractinian coral species (Seriatopora hystrix, Montipora monasteriata and Acropora echinata) under simulated heat shock bleaching at 34 °C during a time course of 36 h. All three species displayed a similar initial increase of Hsp60 level which accompanies the increasing paleness of coral tissue. Afterwards, each of them showed a specific pattern of Hsp60 down-regulation which can be indicative of a different threshold of resistance, although it proceeded in synchrony with the complete bleaching of tissues. The finely branched S. hystrix was the species most susceptible to heat stress while the plating M. monasteriata was the most tolerant one, as its Hsp60 down-regulation was less rapid than the branching corals. On the whole, the Hsp60 modulation appears useful for providing information about the susceptibility of the different coral taxa to environmental disturbances.

FW-04-806 inhibits proliferation and induces apoptosis in human breast cancer cells by binding to N-terminus of Hsp90 and disrupting Hsp90-Cdc37 complex formation

Background

Heat shock protein 90 (Hsp90) is a promising therapeutic target and inhibition of Hsp90 will presumably result in suppression of multiple signaling pathways. FW-04-806, a bis-oxazolyl macrolide compound extracted from China-native Streptomyces FIM-04-806, was reported to be identical in structure to the polyketide Conglobatin.

Methods

We adopted the methods of chemproteomics, computational docking, immunoprecipitation, siRNA gene knock down, Quantitative Real-time PCR and xenograft models on the research of FW-04-806 antitumor mechanism, through the HER2-overexpressing breast cancer SKBR3 and HER2-underexpressing breast cancer MCF-7 cell line.

Results

We have verified the direct binding of FW-04-806 to the N-terminal domain of Hsp90 and found that FW-04-806 inhibits Hsp90/cell division cycle protein 37 (Cdc37) chaperone/co-chaperone interactions, but does not affect ATP-binding capability of Hsp90, thereby leading to the degradation of multiple Hsp90 client proteins via the proteasome pathway. In breast cancer cell lines, FW-04-806 inhibits cell proliferation, caused G2/M cell cycle arrest, induced apoptosis, and downregulated Hsp90 client proteins HER2, Akt, Raf-1 and their phosphorylated forms (p-HER2, p-Akt) in a dose and time-dependent manner. Importantly, FW-04-806 displays a better anti-tumor effect in HER2-overexpressed SKBR3 tumor xenograft model than in HER2-underexpressed MCF-7 model. The result is consistent with cell proliferation assay and in vitro apoptosis assay applied for SKBR-3 and MCF-7. Furthermore, FW-04-806 has a favorable toxicity profile.

Conclusions

As a novel Hsp90 inhibitor, FW-04-806 binds to the N-terminal of Hsp90 and inhibits Hsp90/Cdc37 interaction, resulting in the disassociation of Hsp90/Cdc37/client complexes and the degradation of Hsp90 client proteins. FW-04-806 displays promising antitumor activity against breast cancer cells both in vitro and in vivo, especially for HER2-overexpressed breast cancer cells.

The hop-like stress-induced protein 1 cochaperone is a novel cell-intrinsic restriction factor for mitochondrial tombusvirus replication

Recent genome-wide screens reveal that the host cells express an arsenal of proteins that inhibit replication of plus-stranded RNA viruses by functioning as cell-intrinsic restriction factors of viral infections. One group of cell-intrinsic restriction factors against tombusviruses contains tetratricopeptide repeat (TPR) domains that directly interact with the viral replication proteins. In this paper, we find that the TPR domain-containing Hop-like stress-inducible protein 1 (Sti1p) cochaperone selectively inhibits the mitochondrial membrane-based replication of Carnation Italian ringspot tombusvirus (CIRV). In contrast, Sti1/Hop does not inhibit the peroxisome membrane-based replication of the closely related Tomato bushy stunt virus (TBSV) or Cucumber necrosis virus (CNV) in a yeast model or in plants. Deletion of STI1 in yeast leads to up to a 4-fold increase in CIRV replication, and knockdown of the orthologous Hop cochaperone in plants results in a 3-fold increase in CIRV accumulation. Overexpression of Sti1p derivatives in yeast reveals that the inhibitory function depends on the TPR1 domain known to interact with heat shock protein 70 (Hsp70), but not on the TPR2 domain interacting with Hsp90. In vitro CIRV replication studies based on isolated mitochondrial preparations and purified recombinant proteins has confirmed that Sti1p, similar to the TPR-containing Cyp40-like Cpr7p cyclophilin and the Ttc4 oncogene-like Cns1 cochaperone, is a strong inhibitor of CIRV replication. Sti1p interacts and colocalizes with the CIRV replication proteins in yeast. Our findings indicate that the TPR-containing Hop/Sti1 cochaperone could act as a cell-intrinsic virus restriction factor of the mitochondrial CIRV, but not against the peroxisomal tombusviruses in yeast and plants.

IMPORTANCE

The host cells express various cell-intrinsic restriction factors that inhibit the replication of plus-stranded RNA viruses. In this paper, the authors find that the Hop-like stress-inducible protein 1 (Sti1p) cochaperone selectively inhibits the mitochondrial membrane-based replication of Carnation Italian ringspot tombusvirus (CIRV) in yeast. Deletion of STI1 in yeast or knockdown of the orthologous Hop cochaperone in plants leads to increased CIRV replication. In addition, overexpression of Sti1p derivatives in yeast reveals that the inhibitory function depends on the TPR1 domain known to interact with heat shock protein 70 (Hsp70), but not on the TPR2 domain interacting with Hsp90. In vitro CIRV replication studies based on isolated mitochondrial preparations and purified recombinant proteins have confirmed that Sti1p is a strong inhibitor of CIRV replication. The authors' findings reveal that the Hop/Sti1 cochaperone could act as a cell-intrinsic restriction factor against the mitochondrial CIRV, but not against the related peroxisomal tombusviruses.

Biochemical characterization and role of the proteasome in the oxidative stress response of adult Schistosoma mansoni worms

The trematode Schistosoma mansoni, an important parasite of humans, is the principle agent of the disease schistosomiasis. In the human host, one of the most important stress factors of this parasite is the oxidative stress generated by both the metabolism of the worm and the immune system of the host. The proteasomal system is responsible for protein homeostasis during oxidative stress. The 26S proteasome is a multicatalytic protease formed by two compartments, a 20S core and regulatory particle 19S, and controls the degradation of intracellular proteins, hence regulating many cellular processes. In the present report, we describe the biochemical characterization and role of the 20S proteasome in the response of adult S. mansoni worms exposed to hydrogen peroxide. Characterization of the response to the oxidative stress included the evaluation of viability, egg production, mortality, tegument integrity, and both expression and activity of proteasome. We observed decreases in viability, egg production as well as 100% mortality at the higher concentrations of hydrogen peroxide tested. The main changes observed in the tegument of adult worms were peeling as well as the appearance of bubbles and a decrease of spines on the tubercles. Furthermore, there were increases in 26S activity to the same extent as 20S proteasome activity, although there was increase of 20S proteasome content, suggesting that degradation of protein oxidized in adult worms is due to the 20S proteasome. It was demonstrated that adult S. mansoni worms are sensitive to oxidative stress, and that a variety of processes in this parasite are altered under this condition. The work contributes to a better understanding of the mechanisms employed by S. mansoni to survive under oxidative stress.

HSP27, 70 and 90, anti-apoptotic proteins, in clinical cancer therapy (Review)

Among the heat shock proteins (HSP), HSP27, HSP70 and HSP90 are the most studied stress-inducible HSPs, and are induced in response to a wide variety of physiological and environmental insults, thus allowing cells to survive to lethal conditions based on their powerful cytoprotective functions. Different functions of HSPs have been described to explain their cytoprotective functions, including their most basic role as molecular chaperones, that is to regulate protein folding, transport, translocation and assembly, especially helping in the refolding of misfolded proteins, as well as their anti-apoptotic properties. In cancer cells, the expression and/or activity of the three HSPs is abnormally high, and is associated with increased tumorigenicity, metastatic potential of cancer cells and resistance to chemotherapy. Associating with key apoptotic factors, they are powerful anti-apoptotic proteins, having the capacity to block the cell death process at different levels. Altogether, the properties suggest that HSP27, HSP70 and HSP90 are appropriate targets for modulating cell death pathways. In this review, we summarize the role of HSP90, HSP70 and HSP27 in apoptosis and the emerging strategies that have been developed for cancer therapy based on the inhibition of the three HSPs.

Asymmetric Hsp90 N domain SUMOylation recruits Aha1 and ATP-competitive inhibitors

The stability and activity of numerous signaling proteins in both normal and cancer cells depends on the dimeric molecular chaperone heat shock protein 90 (Hsp90). Hsp90's function is coupled to ATP binding and hydrolysis and requires a series of conformational changes that are regulated by cochaperones and numerous posttranslational modifications (PTMs). SUMOylation is one of the least-understood Hsp90 PTMs. Here, we show that asymmetric SUMOylation of a conserved lysine residue in the N domain of both yeast (K178) and human (K191) Hsp90 facilitates both recruitment of the adenosine triphosphatase (ATPase)-activating cochaperone Aha1 and, unexpectedly, the binding of Hsp90 inhibitors, suggesting that these drugs associate preferentially with Hsp90 proteins that are actively engaged in the chaperone cycle. Importantly, cellular transformation is accompanied by elevated steady-state N domain SUMOylation, and increased Hsp90 SUMOylation sensitizes yeast and mammalian cells to Hsp90 inhibitors, providing a mechanism to explain the sensitivity of cancer cells to these drugs.

Sparse labeling of proteins: structural characterization from long range constraints

Structural characterization of biologically important proteins faces many challenges associated with degradation of resolution as molecular size increases and loss of resolution improving tools such as perdeuteration when non-bacterial hosts must be used for expression. In these cases, sparse isotopic labeling (single or small subsets of amino acids) combined with long range paramagnetic constraints and improved computational modeling offer an alternative. This perspective provides a brief overview of this approach and two discussions of potential applications; one involving a very large system (an Hsp90 homolog) in which perdeuteration is possible and methyl-TROSY sequences can potentially be used to improve resolution, and one involving ligand placement in a glycosylated protein where resolution is achieved by single amino acid labeling (the sialyltransferase, ST6Gal1). This is not intended as a comprehensive review, but as a discussion of future prospects that promise impact on important questions in the structural biology area.

Mycobacterium leprae Hsp65 administration reduces the lifespan of aged high antibody producer mice

BACKGROUND

Aging process may result in immune modifications that lead to disruption of innate and acquired immunity mechanisms that may induce chronic-degenerative events. The heat shock proteins (Hsp), phylogeneticaly conserved among organisms, present as main function the ability of folding and refolding proteins, but they also are associated with chronic-degenerative disorders. Here were evaluated the role of M. leprae native Hsp65 (WT) and its point-mutated (K409A) on survival and anti-DNA and anti-Hsp65 antibody production of aged genetically selected mice for high (HIII) and low (LIII) antibody production; data from 120- and 270-days old mice (named "adult" or "aged", respectively) were compared.

RESULTS

WT Hsp65 administration induces reduction in the mean survival time of adult and aged female HIII mice, this effect being stronger in aged individuals. Surprisingly, the native protein administration increased the survival of aged female LIII when compared to K409A and control groups. No survival differences were observed in aged male mice after Hsp65 proteins inoculation. We observed increase in IgG1 anti-Hsp65 in WT and K409A aged HIII female mice groups and no marked changes in the anti-DNA (adult and aged HIII) and anti-Hsp65 IgG1 or IgG2a isotypes production in adult HIII female and aged male mice. LIII male mice presented increased anti-DNA and anti-Hsp65 IgG2a isotype production after WT or K409A injection, and LIII female groups showed no alterations.

CONCLUSIONS

The results revealed that the WT Hsp65 interferes with survival of aged HIII female mice without involvement of a remarkable IgG1 and IgG2a anti-DNA and anti-Hsp65 antibodies production. The deleterious effects of Hsp65 on survival time in aged HIII female mice could be linked to a gender-effect and are in agreement with those previously reported in lupus-prone mice.

ATP requirement for chloroplast protein import is set by the Km for ATP hydrolysis of stromal Hsp70 in Physcomitrella patens

The 70-kD family of heat shock proteins (Hsp70s) is involved in a number of seemingly disparate cellular functions, including folding of nascent proteins, breakup of misfolded protein aggregates, and translocation of proteins across membranes. They act through the binding and release of substrate proteins, accompanied by hydrolysis of ATP. Chloroplast stromal Hsp70 plays a crucial role in the import of proteins into plastids. Mutations of an ATP binding domain Thr were previously reported to result in an increase in the Km for ATP and a decrease in the enzyme's kcat. To ask which chloroplast stromal chaperone, Hsp70 or Hsp93, both of which are ATPases, dominates the energetics of the motor responsible for protein import, we made transgenic moss (Physcomitrella patens) harboring the Km-altering mutation in the essential stromal Hsp70-2 and measured the effect on the amount of ATP required for protein import into chloroplasts. Here, we report that increasing the Km for ATP hydrolysis of Hsp70 translated into an increased Km for ATP usage by chloroplasts for protein import. This thus directly demonstrates that the ATP-derived energy long known to be required for chloroplast protein import is delivered via the Hsp70 chaperones and that the chaperone's ATPase activity dominates the energetics of the reaction.

Hsp90-Tau complex reveals molecular basis for specificity in chaperone action

Protein folding in the cell relies on the orchestrated action of conserved families of molecular chaperones, the Hsp70 and Hsp90 systems. Hsp70 acts early and Hsp90 late in the folding path, yet the molecular basis of this timing is enigmatic, mainly because the substrate specificity of Hsp90 is poorly understood. Here, we obtained a structural model of Hsp90 in complex with its natural disease-associated substrate, the intrinsically disordered Tau protein. Hsp90 binds to a broad region in Tau that includes the aggregation-prone repeats. Complementarily, a 106-Å-long substrate-binding interface in Hsp90 enables many low-affinity contacts. This allows recognition of scattered hydrophobic residues in late folding intermediates that remain after early burial of the Hsp70 sites. Our model resolves the paradox of how Hsp90 specifically selects for late folding intermediates but also for some intrinsically disordered proteins-through the eyes of Hsp90 they look the same.

ATPase activity and ATP-dependent conformational change in the co-chaperone HSP70/HSP90-organizing protein (HOP)

Co-chaperones help to maintain cellular homeostasis by modulating the activities of molecular chaperones involved in protein quality control. The HSP70/HSP90-organizing protein (HOP) is a co-chaperone that cooperates with HSP70 and HSP90 in catalysis of protein folding and maturation in the cytosol. We show here that HOP has ATP-binding activity comparable to that of HSP70/HSP90, and that HOP slowly hydrolyzes ATP. Analysis of deletion mutants revealed that the ATPase domain of HOP is in the N-terminal TPR1-DP1-TPR2A segment. In addition, HOP changes its conformation in the presence of ATP. These results indicate that HOP is a unique co-chaperone that undergoes an ATP-dependent conformational change.

Direct assessment in bacteria of prionoid propagation and phenotype selection by Hsp70 chaperone

Protein amyloid aggregates epigenetically determine either advantageous or proteinopathic phenotypes. Prions are infectious amyloidogenic proteins, whereas prionoids lack infectivity but spread from mother to daughter cells. While prion amyloidosis has been studied in yeast and mammalian cells models, the dynamics of transmission of an amyloid proteinopathy has not been addressed yet in bacteria. Using time-lapse microscopy and a microfluidic set-up, we have assessed in Escherichia coli the vertical transmission of the amyloidosis caused by the synthetic bacterial model prionoid RepA-WH1 at single cell resolution within their lineage context. We identify in vivo the coexistence of two strain-like types of amyloid aggregates within a genetically identical population and a controlled homogeneous environment. The amyloids are either toxic globular particles or single comet-shaped aggregates that split during cytokinesis and exhibit milder toxicity. Both segregate and propagate in sublineages, yet show interconversion. ClpB (Hsp104) chaperone, key for spreading of yeast prions, has no effect on the dynamics of the two RepA-WH1 aggregates. However, the propagation of the comet-like species is DnaK (Hsp70)-dependent. The bacterial RepA-WH1 prionoid thus provides key qualitative and quantitative clues on the biology of intracellular amyloid proteinopathies.

Molecular chaperone functions in protein folding and proteostasis

The biological functions of proteins are governed by their three-dimensional fold. Protein folding, maintenance of proteome integrity, and protein homeostasis (proteostasis) critically depend on a complex network of molecular chaperones. Disruption of proteostasis is implicated in aging and the pathogenesis of numerous degenerative diseases. In the cytosol, different classes of molecular chaperones cooperate in evolutionarily conserved folding pathways. Nascent polypeptides interact cotranslationally with a first set of chaperones, including trigger factor and the Hsp70 system, which prevent premature (mis)folding. Folding occurs upon controlled release of newly synthesized proteins from these factors or after transfer to downstream chaperones such as the chaperonins. Chaperonins are large, cylindrical complexes that provide a central compartment for a single protein chain to fold unimpaired by aggregation. This review focuses on recent advances in understanding the mechanisms of chaperone action in promoting and regulating protein folding and on the pathological consequences of protein misfolding and aggregation.

Protein rescue from aggregates by powerful molecular chaperone machines

Protein quality control within the cell requires the interplay of many molecular chaperones and proteases. When this quality control system is disrupted, polypeptides follow pathways leading to misfolding, inactivity and aggregation. Among the repertoire of molecular chaperones are remarkable proteins that forcibly untangle protein aggregates, called disaggregases. Structural and biochemical studies have led to new insights into how these proteins collaborate with co-chaperones and utilize ATP to power protein disaggregation. Understanding how energy-dependent protein disaggregating machines function is universally important and clinically relevant, as protein aggregation is linked to medical conditions such as Alzheimer's disease, Parkinson's disease, amyloidosis and prion diseases.

Hsp70 positively regulates porcine circovirus type 2 replication in vitro

The Hsp70 chaperone plays a central role in multiple processes within cells. Porcine circovirus type 2 (PCV2) is the essential causal agent of post-weaning multisystemic wasting syndrome (PMWS), which has spread worldwide. But the mechanism of PCV2 replication remains poorly understood. In this study, we firstly found the positive effect of heat stress on the replication of PCV2 in the continuous porcine monocytic cell line 3D4/31. Downregulation of Hsp70 by the specific chaperone inhibitor Quercetin or RNA interference and upregulation of Hsp70 by expression from a recombinant adenovirus showed that Hsp70 enhanced PCV2 genome replication and virion production. A specific interaction between Hsp70 and PCV2 Cap was confirmed by colocalization by confocal microscopy and co-immunoprecipitation. Furthermore, the NF-κB pathway was activated and caspase-3 activity was reduced when Hsp70 was overexpressed in PCV2-infected 3D4/31 cells. These data suggested that Hsp70 positively regulated PCV2 replication, which being helpful for understanding the molecular mechanism of PCV2 infection.

Chaperone machines for protein folding, unfolding and disaggregation

Molecular chaperones are diverse families of multidomain proteins that have evolved to assist nascent proteins to reach their native fold, protect subunits from heat shock during the assembly of complexes, prevent protein aggregation or mediate targeted unfolding and disassembly. Their increased expression in response to stress is a key factor in the health of the cell and longevity of an organism. Unlike enzymes with their precise and finely tuned active sites, chaperones are heavy-duty molecular machines that operate on a wide range of substrates. The structural basis of their mechanism of action is being unravelled (in particular for the heat shock proteins HSP60, HSP70, HSP90 and HSP100) and typically involves massive displacements of 20-30 kDa domains over distances of 20-50 Å and rotations of up to 100°.

Heat shock transcriptional responses in an MC-Producing Cyanobacterium (Planktothrix agardhii) and its MC-deficient mutant under high light conditions

Microcystins (MCs) are the most commonly-reported hepatotoxins produced by various cyanobacterial taxa in fresh waters to constitute a potential threat to human and animal health. The biological role of MCs in the producer organisms is not known, and it would be very useful to understand the driving force behind the toxin production. Recent studies have suggested that MCs may have a protective function in cells facing environmental stress. Following this starting premise, we speculate that under adverse conditions the expression of stress-related genes coding for Heat Shock Proteins (Hsp) might be different in an MC-producing strain and its MC-deficient mutant. We therefore used RT-qPCR to compare the expression of 13 hsp genes of an MC-producing strain of Planktothrix agardhii (CYA126/8) and its MC-deficient ΔmcyD mutant over different periods of exposure to high light stress (HL). Three reference genes (RGs) were selected from six candidates to normalize the RT-qPCR data. Of these three RGs (rsh, rpoD, and gltA), gltA is used here for the first time as an RG in prokaryotes. Under HL stress, five genes were found to be strongly up-regulated in both strains (htpG, dnaK, hspA, groES, and groEL). Unexpectedly, we found that the MC-producing wild type strain accumulated higher levels of htpG and dnaK transcripts in response to HL stress than the MC-deficient mutant. In addition, a significant increase in the mcyE transcript was detected in the mutant, suggesting that MCs are required under HL conditions. We discuss several possible roles of MCs in the response to HL stress through their possible involvement in the protective mechanisms of the cells.

Exploring the effect of salinity changes on the levels of Hsp60 in the tropical coral Seriatopora caliendrum

Osmotic stress represents a limiting physical parameter for marine organisms and especially for sessile scleractinian corals which are known to be basically stenohaline and osmoconformers. The salinity changes may cause important cellular damage since corals lack any developed physiological regulatory system. One mechanism of reaction to deleterious conditions is the rapid increase of the induction of heat shock proteins. This study highlights the modulation of the expression of a mitochondrial heat shock protein, such as the chaperonin Hsp60, in the animal tissues of the scleractinian coral Seriatopora caliendrum under three salinity scenarios (hypersalinity of 45 ppt, hyposalinity of 25 ppt and extreme hyposalinity of 15 ppt). The study was performed during the time course of a 2-day period and accompanied also by the assessment of the coral health condition. For each salinity stress S. caliendrum responds differently at the morphological and cellular levels, since the Hsp60 exhibited specific patterns of expression and the coral showed different tissue appearance. Furthermore, the response reflects the severity and exposure length of the disturbance. However, the results indicate that S. caliendrum seems able to tolerates high salinity better than low salinity. In particular, in extreme hyposalinity conditions, a considerable gradual down-regulation of Hsp60 was detected accompanied by necrosis and degradation of the coral tissues. The study suggests that Hsp60 may be involved in the mechanisms of cellular response to stress caused by exposure to adverse salinity.

Experimental and structural testing module to analyze paralogue-specificity and affinity in the Hsp90 inhibitors series

We here describe the first reported comprehensive analysis of Hsp90 paralogue affinity and selectivity in the clinical Hsp90 inhibitor chemotypes. This has been possible through the development of a versatile experimental assay based on a new FP-probe (16a) that we both describe here. The assay can test rapidly and accurately the binding affinity of all major Hsp90 chemotypes and has a testing range that spans low nanomolar to millimolar binding affinities. We couple this assay with a computational analysis that allows for rationalization of paralogue selectivity and defines not only the major binding modes that relay pan-paralogue binding or, conversely, paralogue selectivity, but also identifies molecular characteristics that impart such features. The methods developed here provide a blueprint for parsing out the contribution of the four Hsp90 paralogues to the perceived biological activity with the current Hsp90 chemotypes and set the ground for the development of paralogue selective inhibitors.

The use of stress-70 proteins in physiology: a re-appraisal

There are few factors more important to the mechanisms of evolution than stress. The stress response has formed as a result of natural selection, improving the capacity of organisms to withstand situations that require action.The ubiquity of the cellular stress response suggests that effective mechanisms to counteract stress emerged early in the history of life, and their commonality proves how vital such mechanisms are to operative evolution. The cellular stress response (CSR) has been identified as a characteristic of cells in all three domains of life and consists of a core 44 proteins that are structurally highly conserved and that have been termed the ‘minimal stressproteome’ (MSP). Within the MSP, the most intensely researched proteins are a family of heat-shock proteins known as HSP70. Superficially, correlations between the induction of stress and HSP70 differential expression support the use of HSP70 expression as a nonspecific biomarker of stress. However, we argue that too often authors have failed to question exactly what HSP70 differential expression signifies. Herein, we argue that HSP70 up-regulation in response to stressors has been shown to be far more complex than the commonly accepted quasi-linear relationship. In addition, in many instances, the uncertain identity and function of heat-shock proteins and heat-shock cognates has led to difficulties in interpretation of reports of inducible heat-shock proteins and constitutive heat-shock cognates. We caution against the broad application of HSP70 as a biomarker of stress in isolation and conclude that the application of HSP70 as a meaningful index of stress requires a higher degree of validation than the majority of research currently undertakes.

SGTA: a new player in the molecular co-chaperone game

Small glutamine-rich tetratricopeptide repeat-containing protein α (SGTA) is a steroid receptor molecular co-chaperone that may substantially influence hormone action and, consequently, hormone-mediated carcinogenesis. To date, published studies describe SGTA as a protein that is potentially critical in a range of biological processes, including viral infection, cell division, mitosis, and cell cycle checkpoint activation. SGTA interacts with the molecular chaperones, heat shock protein 70 (HSP70) and HSP90, and with steroid receptor complexes, including those containing the androgen receptor. Steroid receptors are critical for maintaining cell growth and differentiation in hormonally regulated tissues, such as male and female reproductive tissues, and also play a role in disease states involving these tissues. There is growing evidence that, through its interactions with chaperones and steroid receptors, SGTA may be a key player in the pathogenesis of hormonally influenced disease states, including prostate cancer and polycystic ovary syndrome. Research into the function of SGTA has been conducted in several model organisms and cell types, with these studies showing that SGTA functionality is cell-specific and tissue-specific. However, very few studies have been replicated in multiple cell types or experimental systems. Although a broad range of functions have been attributed to SGTA, there is a serious lack of mechanistic information to describe how SGTA acts. In this review, published evidence linking SGTA with hormonally regulated disease states is summarized and discussed, highlighting the need for future research to more clearly define the biological function(s) of this potentially important co-chaperone.

Conformational and functional studies of a cytosolic 90 kDa heat shock protein Hsp90 from sugarcane

Hsp90s are involved in several cellular processes, such as signaling, proteostasis, epigenetics, differentiation and stress defense. Although Hsp90s from different organisms are highly similar, they usually have small variations in conformation and function. Thus, the characterization of different Hsp90s is important to gain insight into the structure-function relationship that makes these chaperones key regulators in protein homeostasis. This work describes the characterization of a cytosolic Hsp90 from sugarcane and its comparison with Hsp90s from other plants. Previous expressed sequence tag (EST) studies in Saccharum spp. (sugarcane) predicted the presence of an mRNA coding for a cytosolic Hsp90. The corresponding cDNA was cloned, and the recombinant protein was purified and its conformation and function characterized. The structural conformation of Hsp90 was assessed by chemical cross-linking and hydrogen/deuterium exchange using mass spectrometry and hydrodynamic assays, which revealed regions accessible to solvent and that Hsp90 is an elongated dimer in solution. The in vivo expression of Hsp90 in sugarcane leaves was confirmed by western blot, and in vitro functional characterization indicated that sugarcane Hsp90 has strong chaperone activity.

Structure and function of Hip, an attenuator of the Hsp70 chaperone cycle

The Hsp70-interacting protein, Hip, cooperates with the chaperone Hsp70 in protein folding and prevention of aggregation. Hsp70 interacts with non-native protein substrates in an ATP-dependent reaction cycle regulated by J-domain proteins and nucleotide exchange factors (NEFs). Hip is thought to delay substrate release by slowing ADP dissociation from Hsp70. Here we present crystal structures of the dimerization domain and the tetratricopeptide repeat (TPR) domain of rat Hip. As shown in a cocrystal structure, the TPR core of Hip interacts with the Hsp70 ATPase domain through an extensive interface, to form a bracket that locks ADP in the binding cleft. Hip and NEF binding to Hsp70 are mutually exclusive, and thus Hip attenuates active cycling of Hsp70-substrate complexes. This mechanism explains how Hip enhances aggregation prevention by Hsp70 and facilitates transfer of specific proteins to downstream chaperones or the proteasome.

Interaction of p53 with the CCT complex promotes protein folding and wild-type p53 activity

p53 is a transcription factor that mediates tumor suppressor responses. Correct folding of the p53 protein is essential for these activities, and point mutations that induce conformational instability of p53 are frequently found in cancers. These mutant p53s not only lose wild-type activity but can also acquire the ability to promote invasion and metastasis. We show that folding of wild-type p53 is promoted by an interaction with the chaperonin CCT. Depletion of this chaperone in cells results in the accumulation of misfolded p53, leading to a reduction in p53-dependent gene expression. Intriguingly, p53 proteins mutated to prevent the interaction with CCT show conformational instability and acquire an ability to promote invasion and random motility that is similar to the activity of tumor-derived p53 mutants. Our data therefore suggest that both growth suppression and cell invasion may be differentially regulated functions of wild-type p53.

Applying chaperones to protein-misfolding disorders: molecular chaperones against α-synuclein in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the accumulation of a protein called α-synuclein (α-syn) into inclusions known as lewy bodies (LB) within neurons. This accumulation is also due to insufficient formation and activity of dopamine produced in certain neurons within the substantia nigra. Lewy bodies are the pathological hallmark of the idiopathic disorder and the cascade that allows α-synuclein to misfold, aggregate and form these inclusions has been the subject of intensive research. Targeting these early steps of oligomerization is one of the main therapeutic approaches in order to develop neurodegenerative-modifying agents. Because the folding and refolding of alpha synuclein is the key point of this cascade, we are interested in this review to summarize the role of some molecular chaperones proteins such as Hsp70, Hsp90 and small heat shock proteins (sHsp) and Hsp 104. Hsp70 and its co-chaperone, Hsp70 and small heat shock proteins can prevent neurodegeneration by preventing α-syn misfolding, oligomerization and aggregation in vitro and in Parkinson disease animal models. Hsp104 is able to resolve disordered protein aggregates and cross beta amyloid conformers. Together, these chaperones have a complementary effect and can be a target for therapeutic intervention in PD.

Allosteric opening of the polypeptide-binding site when an Hsp70 binds ATP

The 70-kilodalton (kDa) heat-shock proteins (Hsp70s) are ubiquitous molecular chaperones essential for cellular protein folding and proteostasis. Each Hsp70 has two functional domains: a nucleotide-binding domain (NBD), which binds and hydrolyzes ATP, and a substrate-binding domain (SBD), which binds extended polypeptides. NBD and SBD interact little when in the presence of ADP; however, ATP binding allosterically couples the polypeptide- and ATP-binding sites. ATP binding promotes polypeptide release; polypeptide rebinding stimulates ATP hydrolysis. This allosteric coupling is poorly understood. Here we present the crystal structure of an intact ATP-bound Hsp70 from Escherichia coli at 1.96-Å resolution. The ATP-bound NBD adopts a unique conformation, forming extensive interfaces with an SBD that has changed radically, having its α-helical lid displaced and the polypeptide-binding channel of its β-subdomain restructured. These conformational changes, together with our biochemical assays, provide a structural explanation for allosteric coupling in Hsp70 activity.

Molecular chaperones as enzymes that catalytically unfold misfolded polypeptides

Stress-denatured or de novo synthesized and translocated unfolded polypeptides can spontaneously reach their native state without assistance of other proteins. Yet, the pathway to native folding is complex, stress-sensitive and prone to errors. Toxic misfolded and aggregated conformers may accumulate in cells and lead to degenerative diseases. Members of the canonical conserved families of molecular chaperones, Hsp100s, Hsp70/110/40s, Hsp60/CCTs, the small Hsps and probably also Hsp90s, can recognize and bind with high affinity, abnormally exposed hydrophobic surfaces on misfolded and aggregated polypeptides. Binding to Hsp100, Hsp70, Hsp110, Hsp40, Hsp60, CCTs and Trigger factor may cause partial unfolding of the misfolded polypeptide substrates, and ATP hydrolysis can induce further unfolding and release from the chaperone, leading to spontaneous refolding into native proteins with low-affinity for the chaperones. Hence, specific chaperones act as catalytic polypeptide unfolding isomerases, rerouting cytotoxic misfolded and aggregated polypeptides back onto their physiological native refolding pathway, thus averting the onset of protein conformational diseases.

Information theory, gene expression, and combinatorial regulation: a quantitative analysis

According to a functional definition of the term "gene", a protein-coding gene corresponds to a polypeptide and, hence, a coding sequence. It is therefore as such not yet present at the DNA level, but assembled from possibly heterogeneous pieces in the course of RNA processing. Assembly and regulation of genes require, thus, information about when and in which quantity specific polypeptides are to be produced. To assess this, we draw upon precise biochemical data. On the basis of our conceptual framework, we also develop formal models for the coordinated expression of specific sets of genes through the interaction of transcripts and mRNAs and with proteins via a precise putative regulatory code. Thus, the nucleotides in transcripts and mRNA are not only arranged into amino acid-coding triplets, but at the same time may participate in regulatory oligomotifs that provide binding sites for specific proteins. We can then quantify and compare product and regulatory information involved in gene expression and regulation.

A role for HMGB1, HSP60 and Myd88 in growth of murine mammary carcinoma in vitro

Previously we reported that Myd88 contributed to tumor progression. To begin to decipher what may be inducing Myd88 dependent signaling we focused on proteins that could function as damage associated molecular pattern molecules (DAMPs) since DAMPs have been reported to be secreted by tumors, and certain DAMPs mediate effects through toll-like receptors. A screen of mammary carcinoma for DAMP expression showed HMGB1 and HSP60 were significantly elevated relative to normal mammary epithelium, and targeting these DAMPs, or receptors for these DAMPs influenced growth of tumor cells. Moreover, analysis using a Myd88 inhibitory peptide suggested that HMGB1 mediated its effects in a Myd88 dependent manner, and inhibiting Myd88 function decreased HMGB1 and HSP60 gene expression. Collectively, these data suggest that HMGB1 and HSP60 contribute to growth of mammary carcinoma cells, HMGB1 accomplishes this, at least in part, through Myd88 dependent signaling, and these DAMPs are expressed in a Myd88 dependent manner.

Evidence on the pathogenic role of auto-antibodies in acute cardiovascular diseases

Atherothrombosis is the major determinant of acute ischaemic cardiovascular events, such as myocardial infarction and stroke. Inflammatory processes have been linked to all phases of atherogenesis In particular, the identification of autoimmunity mediators in the complex microenvironment of chronic inflammation has become the focus of attention in both early and advanced atherogenic processes. Auto-antibodies against self-molecules or new epitopes generated by oxidative processes infiltrate atherosclerotic plaques and were shown to modulate the activity of immune cells by binding various types of receptors. However, despite mounting evidence for a pathophysiological role of autoantibodies in atherothrombosis, the clinical relevance for circulating autoantibodies in cardiovascular outcomes is still debated. This review aims at illustrating the mechanisms by which different types of autoantibodies might either promote or repress atherothrombosis and to discuss the clinical studies assessing the role of auto-antibodies as prognostic biomarkers of plaque vulnerability.

Real-time observation of the conformational dynamics of mitochondrial Hsp70 by spFRET

The numerous functions of the important class of molecular chaperones, heat shock proteins 70 (Hsp70), rely on cycles of intricate conformational changes driven by ATP-hydrolysis and regulated by cochaperones and substrates. Here, we used Förster resonance energy transfer to study the conformational dynamics of individual molecules of Ssc1, a mitochondrial Hsp70, in real time. The intrinsic dynamics of the substrate-binding domain of Ssc1 was observed to be uncoupled from the dynamic interactions between substrate- and nucleotide-binding domains. Analysis of the fluctuations in the interdomain separation revealed frequent transitions to a nucleotide-free state. The nucleotide-exchange factor Mge1 did not induce ADP release, as expected, but rather facilitated binding of ATP. These results indicate that the conformational cycle of Ssc1 is more elaborate than previously thought and provide insight into how the Hsp70s can perform a wide variety of functions.

Influence of specific HSP70 domains on fibril formation of the yeast prion protein Ure2

Ure2p is the protein determinant of the Saccharomyces cerevisiae prion state [URE3]. Constitutive overexpression of the HSP70 family member SSA1 cures cells of [URE3]. Here, we show that Ssa1p increases the lag time of Ure2p fibril formation in vitro in the presence or absence of nucleotide. The presence of the HSP40 co-chaperone Ydj1p has an additive effect on the inhibition of Ure2p fibril formation, whereas the Ydj1p H34Q mutant shows reduced inhibition alone and in combination with Ssa1p. In order to investigate the structural basis of these effects, we constructed and tested an Ssa1p mutant lacking the ATPase domain, as well as a series of C-terminal truncation mutants. The results indicate that Ssa1p can bind to Ure2p and delay fibril formation even in the absence of the ATPase domain, but interaction of Ure2p with the substrate-binding domain is strongly influenced by the C-terminal lid region. Dynamic light scattering, quartz crystal microbalance assays, pull-down assays and kinetic analysis indicate that Ssa1p interacts with both native Ure2p and fibril seeds, and reduces the rate of Ure2p fibril elongation in a concentration-dependent manner. These results provide new insights into the structural and mechanistic basis for inhibition of Ure2p fibril formation by Ssa1p and Ydj1p.

Sequential duplications of an ancient member of the DnaJ-family expanded the functional chaperone network in the eukaryotic cytosol

Across eukaryotes, Hsp70-based chaperone machineries display an underlying unity in their sequence, structure, and biochemical mechanism of action, while working in a myriad of cellular processes. In good part, this extraordinary functional versatility is derived from the ability of a single Hsp70 to interact with an array of J-protein cochaperones to form a functional chaperone network. Among J-proteins, the DnaJ-type is the most prevalent, being present in all three kingdoms and in several different compartments of eukaryotic cells. However, because these ancient DnaJ-type proteins diverged at the base of the eukaryotic phylogeny, little is understood about the evolutionary basis of their diversification and thus the functional expansion of the chaperone network. Here, we report results of evolutionary and experimental analyses of two more recent members of the cytosolic DnaJ family of Saccharomyces cerevisiae, Xdj1 and Apj1, which emerged by sequential duplications of the ancient YDJ1 in Ascomycota. Sequence comparison and molecular modeling revealed that both Xdj1 and Apj1 maintained a domain organization similar to that of multifunctional Ydj1. However, despite these similarities, both Xdj1 and Apj1 evolved highly specialized functions. Xdj1 plays a unique role in the translocation of proteins from the cytosol into mitochondria. Apj1's specialized role is related to degradation of sumolyated proteins. Together these data provide the first clear example of cochaperone duplicates that evolved specialized functions, allowing expansion of the chaperone functional network, while maintaining the overall structural organization of their parental gene.

Allostery in the Hsp70 chaperone proteins

Heat shock 70-kDa (Hsp70) chaperones are essential to in vivo protein folding, protein transport, and protein re-folding. They carry out these activities using repeated cycles of binding and release of client proteins. This process is under allosteric control of nucleotide binding and hydrolysis. X-ray crystallography, NMR spectroscopy, and other biophysical techniques have contributed much to the understanding of the allosteric mechanism linking these activities and the effect of co-chaperones on this mechanism. In this chapter these findings are critically reviewed. Studies on the allosteric mechanisms of Hsp70 have gained enhanced urgency, as recent studies have implicated this chaperone as a potential drug target in diseases such as Alzheimer's and cancer. Recent approaches to combat these diseases through interference with the Hsp70 allosteric mechanism are discussed.

Molecular mechanism of allosteric communication in Hsp70 revealed by molecular dynamics simulations

Investigating ligand-regulated allosteric coupling between protein domains is fundamental to understand cell-life regulation. The Hsp70 family of chaperones represents an example of proteins in which ATP binding and hydrolysis at the Nucleotide Binding Domain (NBD) modulate substrate recognition at the Substrate Binding Domain (SBD). Herein, a comparative analysis of an allosteric (Hsp70-DnaK) and a non-allosteric structural homolog (Hsp110-Sse1) of the Hsp70 family is carried out through molecular dynamics simulations, starting from different conformations and ligand-states. Analysis of ligand-dependent modulation of internal fluctuations and local deformation patterns highlights the structural and dynamical changes occurring at residue level upon ATP-ADP exchange, which are connected to the conformational transition between closed and open structures. By identifying the dynamically responsive protein regions and specific cross-domain hydrogen-bonding patterns that differentiate Hsp70 from Hsp110 as a function of the nucleotide, we propose a molecular mechanism for the allosteric signal propagation of the ATP-encoded conformational signal.

Allostery, or the capability of proteins to respond to ligand binding events with a variation in structure or dynamics at a distant site, is a common feature for biomolecular function and regulation in a large number of proteins. Intra-protein connections and inter-residue coordinations underlie allosteric mechanisms and react to binding primarily through a finely tuned modulation of motions and structures at the microscopic scale. Hence, all-atom molecular dynamics simulations are suitable to investigate the molecular basis of allostery. Moreover, understanding intra-protein communication pathways at atomistic resolutions offers unique opportunities in rational drug design. Proteins of the Hsp70 family are allosteric molecular chaperones involved in maintaining cellular protein homeostasis. These proteins are involved in several types of cancer, neurodegenerative diseases, aging and infections and are therefore pharmaceutically relevant targets. In this work we have analyzed, by multiple molecular dynamics simulations, the long-range dynamical and conformational effects of ligands bound to Hsp70, and found relevant differences in comparison to the known non-allosteric structural homolog Hsp110. The resulting model of the mechanism of allosteric propagation offers the opportunity of identifying on-pathway allosteric druggable sites, which we propose could guide rational drug-design efforts targeting Hsp70.

Conformational selection in substrate recognition by Hsp70 chaperones

Hsp70s are molecular chaperones involved in the folding and assembly of proteins. They recognize hydrophobic amino acid stretches in their substrate binding groove. However, a detailed understanding of substrate specificity is still missing. Here, we use the endoplasmic reticulum-resident Hsp70 BiP to identify binding sites in a natural client protein. Two sites are mutually recognized and form stable Hsp70-substrate complexes. In silico and in vitro analyses revealed an extended substrate conformation as a crucial factor for interaction and show an unexpected plasticity of the substrate binding groove. The basic binding mechanism is conserved among different Hsp70s.