RESUMO
The highly conserved Hsp90 chaperones control stability and activity of many essential signaling and regulatory proteins including many protein kinases, E3 ligases and transcription factors. Thereby, Hsp90s couple cellular homeostasis of the proteome to cell fate decisions. High-throughput mass spectrometry revealed 178 and 169 posttranslational modifications (PTMs) for human cytosolic Hsp90α and Hsp90ß, but for only a few of the modifications the physiological consequences are investigated in some detail. In this study, we explored the suitability of the yeast model system for the identification of key regulatory residues in human Hsp90α. Replacement of three tyrosine residues known to be phosphorylated by phosphomimetic glutamate and by non-phosphorylatable phenylalanine individually and in combination influenced yeast growth and the maturation of 7 different Hsp90 clients in distinct ways. Furthermore, wild-type and mutant Hsp90 differed in their ability to stabilize known clients when expressed in HepG2 HSP90AA1-/- cells. The purified mutant proteins differed in their interaction with the cochaperones Aha1, Cdc37, Hop and p23 and in their support of the maturation of glucocorticoid receptor ligand binding domain in vitro. In vivo and in vitro data correspond well to each other confirming that the yeast system is suitable for the identification of key regulatory sites in human Hsp90s. Our findings indicate that even closely related clients are affected differently by the amino acid replacements in the investigated positions, suggesting that PTMs could bias Hsp90's client specificity.
RESUMO
The heat shock transcription factors heat shock transcription factor 1 and Hsf2 have been studied for many years, mainly in the context of stress response and in malignant cells. Their physiological function in nonmalignant human cells under nonstress conditions is still largely unknown. To approach this important issue, Joutsen et al. present immunohistochemical staining data on Hsf1 and Hsf2 in 80 nonpathological human tissue samples. The wealth of these data elicits many interesting questions that will spur many future research projects.
Assuntos
Fatores de Transcrição de Choque Térmico , Imuno-Histoquímica , Humanos , Fatores de Transcrição de Choque Térmico/metabolismo , Fatores de Transcrição de Choque Térmico/genética , Imuno-Histoquímica/métodos , Fatores de Transcrição/metabolismo , Proteínas de Ligação a DNA/metabolismo , Proteínas de Choque Térmico/metabolismoRESUMO
Preserving and regulating cellular homeostasis in the light of changing environmental conditions or developmental processes is of pivotal importance for single cellular and multicellular organisms alike. To counteract an imbalance in cellular homeostasis transcriptional programs evolved, called the heat shock response, unfolded protein response, and integrated stress response, that act cell-autonomously in most cells but in multicellular organisms are subjected to cell-nonautonomous regulation. These transcriptional programs downregulate the expression of most genes but increase the expression of heat shock genes, including genes encoding molecular chaperones and proteases, proteins involved in the repair of stress-induced damage to macromolecules and cellular structures. Sixty-one years after the discovery of the heat shock response by Ferruccio Ritossa, many aspects of stress biology are still enigmatic. Recent progress in the understanding of stress responses and molecular chaperones was reported at the 12th International Symposium on Heat Shock Proteins in Biology, Medicine and the Environment in the Old Town Alexandria, VA, USA from 28th to 31st of October 2023.
Assuntos
Proteínas de Choque Térmico , Medicina , Biologia , Proteínas de Choque Térmico/metabolismo , Resposta ao Choque Térmico/genética , Chaperonas Moleculares/metabolismoRESUMO
J-domain proteins (JDPs) are the largest family of chaperones in most organisms, but much of how they function within the network of other chaperones and protein quality control machineries is still an enigma. Here, we report on the latest findings related to JDP functions presented at a dedicated JDP workshop in Gdansk, Poland. The report does not include all (details) of what was shared and discussed at the meeting, because some of these original data have not yet been accepted for publication elsewhere or represented still preliminary observations at the time.
Assuntos
Proteínas de Choque Térmico HSP70 , Chaperonas Moleculares , Proteínas de Choque Térmico HSP70/metabolismo , Chaperonas Moleculares/metabolismo , Polônia , Proteínas de Choque Térmico HSP40/metabolismoRESUMO
Protein glycosylation is an essential post-translational modification in all domains of life. Its impairment in humans can result in severe diseases named congenital disorders of glycosylation (CDGs). Most of the glycosyltransferases (GTs) responsible for proper glycosylation are polytopic membrane proteins that represent challenging targets in proteomics. We established a multiple reaction monitoring (MRM) assay to comprehensively quantify GTs involved in the processes of N-glycosylation and O- and C-mannosylation in the endoplasmic reticulum. High robustness was achieved by using an enriched membrane protein fraction of isotopically labeled HEK 293T cells as an internal protein standard. The analysis of primary skin fibroblasts from eight CDG type I patients with impaired ALG1, ALG2, and ALG11 genes, respectively, revealed a substantial reduction in the corresponding protein levels. The abundance of the other GTs, however, remained unchanged at the transcript and protein levels, indicating that there is no fail-safe mechanism for the early steps of glycosylation in the endoplasmic reticulum. The established MRM assay was shared with the scientific community via the commonly used open source Skyline software environment, including Skyline Batch for automated data analysis. We demonstrate that another research group could easily reproduce all analysis steps, even while using different LC-MS hardware.
Assuntos
Defeitos Congênitos da Glicosilação , Glicosiltransferases , Humanos , Glicosilação , Glicosiltransferases/genética , Defeitos Congênitos da Glicosilação/genética , Proteômica , Processamento de Proteína Pós-Traducional , Proteínas de Membrana/genética , ManosiltransferasesRESUMO
Ubiquitin-specific proteases (USPs) are crucial for controlling cellular proteostasis and signaling pathways but how deubiquitination is selective remains poorly understood, in particular between paralogues. Here, we developed a fusion tag method by mining the Protein Data Bank and trapped USP11, a key regulator of DNA double-strand break repair, in complex with a novel engineered substrate mimetic. Together, this enabled structure determination of USP11 as a Michaelis-like complex that revealed key S1 and S1' binding site interactions with a substrate. Combined mutational, enzymatic, and binding experiments identified Met77 in linear diubiquitin as a significant residue that leads to substrate discrimination. We identified an aspartate "gatekeeper" residue in the S1' site of USP11 as a contributing feature for discriminating against linear diubiquitin. When mutated to a glycine, the corresponding residue in paralog USP15, USP11 acquired elevated activity toward linear diubiquitin in-gel shift assays, but not controls. The reverse mutation in USP15 confirmed that this position confers paralog-specific differences impacting diubiquitin cleavage rates. The results advance our understanding of the molecular basis for the higher selectivity of USP11 compared to USP15 and may aid targeted inhibitor development. Moreover, the reported carrier-based crystallization strategy may be applicable to other challenging targets.
Assuntos
Modelos Moleculares , Proteases Específicas de Ubiquitina , Sítios de Ligação , Proteases Específicas de Ubiquitina/química , Proteases Específicas de Ubiquitina/metabolismo , Humanos , Ubiquitinação/genética , Estrutura Terciária de Proteína , Cristalografia por Raios X , Especificidade por Substrato/genéticaRESUMO
The 70 kDa heat shock proteins (Hsp70s) are highly versatile molecular chaperones that assist in a wide variety of protein-folding processes. They exert their functions by continuously cycling between states of low and high affinity for client polypeptides, driven by ATP-binding and hydrolysis. This cycling is tuned by cochaperones and clients. Although structures for the high and low client affinity conformations of Hsp70 and Hsp70 domains in complex with various cochaperones and peptide clients are available, it is unclear how structural rearrangements in the presence of cochaperones and clients are orchestrated in space and time. Here, we report insights into the conformational dynamics of the prokaryotic model Hsp70 DnaK throughout its adenosine-5'-triphosphate hydrolysis (ATPase) cycle using proximity-induced fluorescence quenching. Our data suggest that ATP and cochaperone-induced structural rearrangements in DnaK occur in a sequential manner and resolve hitherto unpredicted cochaperone and client-induced structural rearrangements. Peptides induce large conformational changes in DnaK·ATP prior to ATP hydrolysis, whereas a protein client induces significantly smaller changes but is much more effective in stimulating ATP hydrolysis. Analysis of the enthalpies of activation for the ATP-induced opening of the DnaK lid in the presence of clients indicates that the lid does not exert an enthalpic pulling force onto bound clients, suggesting entropic pulling as a major mechanism for client unfolding. Our data reveal important insights into the mechanics, allostery, and dynamics of Hsp70 chaperones. We established a methodology for understanding the link between dynamics and function, Hsp70 diversity, and activity modulation.
Assuntos
Adenosina Trifosfatases , Proteínas de Escherichia coli , Humanos , Adenosina Trifosfatases/metabolismo , Proteínas de Escherichia coli/metabolismo , Proteínas de Choque Térmico HSP70/metabolismo , Chaperonas Moleculares/metabolismo , Trifosfato de Adenosina/metabolismoRESUMO
The chaperone heat shock protein 90 (Hsp90) is well known to undergo important conformational changes, which depend on nucleotide and substrate interactions. Conversely, how the conformations of its unstable and disordered substrates are affected by Hsp90 is difficult to address experimentally yet is central to its function. Here, using optical tweezers, we find that Hsp90 promotes local contractions in unfolded chains that drive their global compaction down to dimensions of folded states. This compaction has a gradual nature while showing small steps, is stimulated by ATP, and performs mechanical work against counteracting forces that expand the chain dimensions. The Hsp90 interactions suppress the formation of larger-scale folded, misfolded, and aggregated structures. The observations support a model in which Hsp90 alters client conformations directly by promoting local intra-chain interactions while suppressing distant ones. We conjecture that chain compaction may be central to how Hsp90 protects unstable clients and cooperates with Hsp70.
Assuntos
Proteínas de Choque Térmico HSP70 , Proteínas de Choque Térmico HSP90 , Humanos , NucleotídeosRESUMO
To thrive and to fulfill their functions, cells need to maintain proteome homeostasis even in the face of adverse environmental conditions or radical restructuring of the proteome during differentiation. At the center of the regulation of proteome homeostasis is an ancient transcriptional mechanism, the so-called heat shock response (HSR), orchestrated in all eukaryotic cells by heat shock transcription factor 1 (Hsf1). As Hsf1 is implicated in aging and several pathologies like cancer and neurodegenerative disorders, understanding the regulation of Hsf1 could open novel therapeutic opportunities. In this review, we discuss the regulation of Hsf1's transcriptional activity by multiple layers of control circuits involving Hsf1 synthesis and degradation, conformational rearrangements and post-translational modifications (PTMs), and molecular chaperones in negative feedback loops.
Assuntos
Resposta ao Choque Térmico , Fatores de Transcrição , Proteínas de Choque Térmico HSP70/metabolismo , Fatores de Transcrição de Choque Térmico/genética , Fatores de Transcrição de Choque Térmico/metabolismo , Chaperonas Moleculares/metabolismo , Processamento de Proteína Pós-Traducional , Fatores de Transcrição/metabolismoRESUMO
The pathology associated with malaria infection is largely due to the ability of infected human RBCs to adhere to a number of receptors on endothelial cells within tissues and organs. This phenomenon is driven by the export of parasite-encoded proteins to the host cell, the exact function of many of which is still unknown. Here we inactivate the function of one of these exported proteins, PFA66, a member of the J-domain protein family. Although parasites lacking this protein were still able to grow in cell culture, we observed severe defects in normal host cell modification, including aberrant morphology of surface knobs, disrupted presentation of the cytoadherence molecule PfEMP1, and a total lack of cytoadherence, despite the presence of the knob associated protein KAHRP. Complementation assays demonstrate that an intact J-domain is required for recovery to a wild-type phenotype and suggest that PFA66 functions in concert with a HSP70 to carry out host cell modification. Strikingly, this HSP70 is likely to be of host origin. ATPase assays on recombinant protein verify a functional interaction between PFA66 and residual host cell HSP70. Taken together, our data reveal a role for PFA66 in host cell modification, strongly implicate human HSP70s as being essential in this process and uncover a new KAHRP-independent molecular factor required for correct knob biogenesis.
Assuntos
Proteínas de Choque Térmico HSP70/metabolismo , Interações Hospedeiro-Parasita/fisiologia , Malária Falciparum/metabolismo , Plasmodium falciparum/patogenicidade , Proteínas de Protozoários/metabolismo , Humanos , Malária Falciparum/parasitologia , Malária Falciparum/patologia , Plasmodium falciparum/metabolismo , VirulênciaRESUMO
The ATP-dependent Hsp70s are evolutionary conserved molecular chaperones that constitute central hubs of the cellular protein quality surveillance network. None of the other main chaperone families (Tig, GroELS, HtpG, IbpA/B, ClpB) have been assigned with a comparable range of functions. Through a multitude of functions Hsp70s are involved in many cellular control circuits for maintaining protein homeostasis and have been recognized as key factors for cell survival. Three mechanistic properties of Hsp70s are the basis for their high versatility. First, Hsp70s bind to short degenerate sequence motifs within their client proteins. Second, Hsp70 chaperones switch in a nucleotide-controlled manner between a state of low affinity for client proteins and a state of high affinity for clients. Third, Hsp70s are targeted to their clients by a large number of cochaperones of the J-domain protein (JDP) family and the lifetime of the Hsp70-client complex is regulated by nucleotide exchange factors (NEF). In this review I will discuss advances in the understanding of the molecular mechanism of the Hsp70 chaperone machinery focusing mostly on the bacterial Hsp70 DnaK and will compare the two other prokaryotic Hsp70s HscA and HscC with DnaK.
RESUMO
The heat shock response is a transcriptional program of organisms to counteract an imbalance in protein homeostasis. It is orchestrated in all eukaryotic cells by heat shock transcription factor 1 (Hsf1). Despite very intensive research, the intricacies of the Hsf1 activation-attenuation cycle remain elusive at a molecular level. Post-translational modifications belong to one of the key mechanisms proposed to adapt the Hsf1 activity to the needs of individual cells, and phosphorylation of Hsf1 at multiple sites has attracted much attention. According to cell biological and proteomics data, Hsf1 is also modified by small ubiquitin-like modifier (SUMO) at several sites. How SUMOylation affects Hsf1 activity at a molecular level is still unclear. Here, we analyzed Hsf1 SUMOylation in vitro with purified components to address questions that could not be answered in cell culture models. In vitro Hsf1 is primarily conjugated at lysine 298 with a single SUMO, though we did detect low-level SUMOylation at other sites. Different SUMO E3 ligases such as protein inhibitor of activated STAT 4 enhanced the efficiency of in vitro modification but did not alter SUMO site preferences. We provide evidence that Hsf1 trimerization and phosphorylation at serines 303 and 307 increases SUMOylation efficiency, suggesting that Hsf1 is SUMOylated in its activated state. Hsf1 can be SUMOylated when DNA bound, and SUMOylation of Hsf1 does neither alter DNA-binding affinity nor affects heat shock cognate 71kDa protein (HSPA8)+DnaJ homolog subfamily B member 1-mediated monomerization of Hsf1 trimers and concomitant dislocation from DNA. We propose that SUMOylation acts at the transcription level of the heat shock response.
Assuntos
Proteínas de Choque Térmico HSC70/genética , Fatores de Transcrição de Choque Térmico/genética , Resposta ao Choque Térmico/genética , Fator de Transcrição STAT4/genética , Sumoilação/genética , Proteínas de Ligação a DNA/genética , Resposta ao Choque Térmico/fisiologia , Homeostase/genética , Humanos , Dobramento de Proteína , Processamento de Proteína Pós-Traducional/genética , Estresse Fisiológico/genética , Enzimas Ativadoras de Ubiquitina/genética , Ubiquitina-Proteína Ligases/genéticaRESUMO
The neuronal protein complexin contains multiple domains that exert clamping and facilitatory functions to tune spontaneous and action potential-triggered synaptic release. We address the clamping mechanism and show that the accessory helix of complexin arrests assembly of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex that forms the core machinery of intracellular membrane fusion. In a reconstituted fusion assay, site- and stage-specific photo-cross-linking reveals that, prior to fusion, the complexin accessory helix laterally binds the membrane-proximal C-terminal ends of SNAP25 and VAMP2. Corresponding complexin interface mutants selectively increase spontaneous release of neurotransmitters in living neurons, implying that the accessory helix suppresses final zippering/assembly of the SNARE four-helix bundle by restraining VAMP2 and SNAP25.
Assuntos
Membrana Celular/metabolismo , Exocitose , Proteína 25 Associada a Sinaptossoma/química , Proteína 25 Associada a Sinaptossoma/metabolismo , Proteína 2 Associada à Membrana da Vesícula/química , Proteína 2 Associada à Membrana da Vesícula/metabolismo , Cálcio/metabolismo , Reagentes de Ligações Cruzadas/química , Humanos , Luz , Fusão de Membrana , Modelos Biológicos , Proteínas Mutantes/metabolismo , Neurônios/metabolismo , Neurotransmissores/metabolismo , Ligação Proteica , Mapeamento de Interação de Proteínas , Estrutura Secundária de Proteína , Proteolipídeos/metabolismo , Sinapses/metabolismo , Vesículas Sinápticas/metabolismoRESUMO
The heat shock response is a universal transcriptional response to proteotoxic stress orchestrated by heat shock transcription factor Hsf1 in all eukaryotic cells. Despite over 40 years of intense research, the mechanism of Hsf1 activity regulation remains poorly understood at the molecular level. In metazoa, Hsf1 trimerizes upon heat shock through a leucine-zipper domain and binds to DNA. How Hsf1 is dislodged from DNA and monomerized remained enigmatic. Here, using purified proteins, we demonstrate that unmodified trimeric Hsf1 is dissociated from DNA in vitro by Hsc70 and DnaJB1. Hsc70 binds to multiple sites in Hsf1 with different affinities. Hsf1 trimers are monomerized by successive cycles of entropic pulling, unzipping the triple leucine-zipper. Starting this unzipping at several protomers of the Hsf1 trimer results in faster monomerization. This process directly monitors the concentration of Hsc70 and DnaJB1. During heat shock adaptation, Hsc70 first binds to a high-affinity site in the transactivation domain, leading to partial attenuation of the response, and subsequently, at higher concentrations, Hsc70 removes Hsf1 from DNA to restore the resting state.
Assuntos
DNA , Proteínas de Choque Térmico HSC70 , Fatores de Transcrição de Choque Térmico , Multimerização Proteica , Animais , Linhagem Celular , DNA/química , DNA/genética , DNA/metabolismo , Proteínas de Choque Térmico HSC70/química , Proteínas de Choque Térmico HSC70/genética , Proteínas de Choque Térmico HSC70/metabolismo , Proteínas de Choque Térmico HSP40/química , Proteínas de Choque Térmico HSP40/genética , Proteínas de Choque Térmico HSP40/metabolismo , Fatores de Transcrição de Choque Térmico/química , Fatores de Transcrição de Choque Térmico/genética , Fatores de Transcrição de Choque Térmico/metabolismo , Humanos , Camundongos , Camundongos Knockout , Domínios ProteicosRESUMO
Dimerization of the small GTPase Arf is prerequisite for the scission of COPI-coated transport vesicles. Here, we quantify the monomer/dimer equilibrium of Arf within the membrane and show that after membrane scission, Arf dimers are restricted to donor membranes. By hydrogen exchange mass spectrometry, we define the interface of activated dimeric Arf within its switch II region. Single amino acid exchanges in this region reduce the propensity of Arf to dimerize. We suggest a mechanism of membrane scission by which the dimeric form of Arf is segregated to the donor membrane. Our data are consistent with the previously reported absence of dimerized Arf in COPI vesicles and could explain the presence of one single scar-like noncoated region in each COPI vesicle.
Assuntos
Fator 1 de Ribosilação do ADP/química , Fator 1 de Ribosilação do ADP/metabolismo , Vesículas Revestidas pelo Complexo de Proteína do Envoltório/metabolismo , Membrana Celular/metabolismo , Multimerização Proteica , Sítios de Ligação , Humanos , Bicamadas Lipídicas/metabolismo , Modelos MolecularesRESUMO
Heat shock protein 70 (HSP70) chaperones play a central role in protein quality control and are crucial for many cellular processes, including protein folding, degradation, and disaggregation. Human HSP70s compose a family of 13 members that carry out their functions with the aid of even larger families of co-chaperones. A delicate interplay between HSP70s and co-chaperone recruitment is thought to determine substrate fate, yet it has been generally assumed that all Hsp70 paralogs have similar activities and are largely functionally redundant. However, here we found that when expressed in human cells, two highly homologous HSP70s, HSPA1A and HSPA1L, have opposing effects on cellular handling of various substrates. For example, HSPA1A reduced aggregation of the amyotrophic lateral sclerosis-associated protein variant superoxide dismutase 1 (SOD1)-A4V, whereas HSPA1L enhanced its aggregation. Intriguingly, variations in the substrate-binding domain of these HSP70s did not play a role in this difference. Instead, we observed that substrate fate is determined by differential interactions of the HSP70s with co-chaperones. Whereas most co-chaperones bound equally well to these two HSP70s, Hsp70/Hsp90-organizing protein (HOP) preferentially bound to HSPA1L, and the Hsp110 nucleotide-exchange factor HSPH2 preferred HSPA1A. The role of HSPH2 was especially crucial for the HSPA1A-mediated reduction in SOD1-A4V aggregation. These findings reveal a remarkable functional diversity at the level of the cellular HSP70s and indicate that this diversity is defined by their affinities for specific co-chaperones such as HSPH2.
Assuntos
Proteínas de Choque Térmico HSP110/química , Proteínas de Choque Térmico HSP70/química , Proteínas de Homeodomínio/química , Agregação Patológica de Proteínas , Superóxido Dismutase-1/química , Proteínas Supressoras de Tumor/química , Substituição de Aminoácidos , Linhagem Celular Tumoral , Células HEK293 , Proteínas de Choque Térmico HSP110/genética , Proteínas de Choque Térmico HSP70/genética , Proteínas de Homeodomínio/genética , Humanos , Mutação de Sentido Incorreto , Superóxido Dismutase-1/genética , Proteínas Supressoras de Tumor/genéticaRESUMO
Coupling of endoplasmic reticulum (ER) stress to dimerisation-dependent activation of the UPR transducer IRE1 is incompletely understood. Whilst the luminal co-chaperone ERdj4 promotes a complex between the Hsp70 BiP and IRE1's stress-sensing luminal domain (IRE1LD) that favours the latter's monomeric inactive state and loss of ERdj4 de-represses IRE1, evidence linking these cellular and in vitro observations is presently lacking. We report that enforced loading of endogenous BiP onto endogenous IRE1α repressed UPR signalling in CHO cells and deletions in the IRE1α locus that de-repressed the UPR in cells, encode flexible regions of IRE1LD that mediated BiP-induced monomerisation in vitro. Changes in the hydrogen exchange mass spectrometry profile of IRE1LD induced by ERdj4 and BiP confirmed monomerisation and were consistent with active destabilisation of the IRE1LD dimer. Together, these observations support a competition model whereby waning ER stress passively partitions ERdj4 and BiP to IRE1LD to initiate active repression of UPR signalling.
Assuntos
Estresse do Retículo Endoplasmático/genética , Endorribonucleases/química , Proteínas de Choque Térmico HSP40/química , Proteínas de Membrana/química , Chaperonas Moleculares/química , Proteínas Serina-Treonina Quinases/química , Resposta a Proteínas não Dobradas/genética , Animais , Células CHO , Cricetinae , Cricetulus , Retículo Endoplasmático/genética , Chaperona BiP do Retículo Endoplasmático , Endorribonucleases/genética , Escherichia coli/genética , Proteínas de Choque Térmico HSP40/genética , Proteínas de Choque Térmico HSP70/química , Proteínas de Choque Térmico HSP70/genética , Humanos , Proteínas de Membrana/genética , Chaperonas Moleculares/genética , Chaperonas Moleculares/metabolismo , Ligação Proteica/genética , Conformação Proteica , Multimerização Proteica/genética , Proteínas Serina-Treonina Quinases/genéticaRESUMO
The cellular protein quality control machinery with its central constituents of chaperones and proteases is vital to maintain protein homeostasis under physiological conditions and to protect against acute stress conditions. Imbalances in protein homeostasis also are keys to a plethora of genetic and acquired, often age-related, diseases as well as aging in general. At the EMBO Workshop, speakers covered all major aspects of cellular protein quality control, from basic mechanisms at the molecular, cellular, and organismal level to medical translation. In this report, the highlights of the meeting will be summarized.
Assuntos
Chaperonas Moleculares/fisiologia , Animais , Células Cultivadas , Homeostase , Humanos , Dobramento de Proteína , Proteostase , Deficiências na Proteostase , EspanhaRESUMO
The 70-kDa heat shock proteins (Hsp70s) are ubiquitous molecular chaperones that act in a large variety of cellular protein folding and remodelling processes. They function virtually at all stages of the life of proteins from synthesis to degradation and are thus crucial for maintaining protein homeostasis, with direct implications for human health. A large set of co-chaperones comprising J-domain proteins and nucleotide exchange factors regulate the ATPase cycle of Hsp70s, which is allosterically coupled to substrate binding and release. Moreover, Hsp70s cooperate with other cellular chaperone systems including Hsp90, Hsp60 chaperonins, small heat shock proteins and Hsp100 AAA+ disaggregases, together constituting a dynamic and functionally versatile network for protein folding, unfolding, regulation, targeting, aggregation and disaggregation, as well as degradation. In this Review we describe recent advances that have increased our understanding of the molecular mechanisms and working principles of the Hsp70 network. This knowledge showcases how the Hsp70 chaperone system controls diverse cellular functions, and offers new opportunities for the development of chemical compounds that modulate disease-related Hsp70 activities.