The Hsp70 (Heat Shock Protein 70 kDa) family represents one of the most conserved and functionally important groups of molecular chaperones in all living organisms. These proteins play critical roles in protein homeostasis, cellular stress responses, and are increasingly recognized as important therapeutic targets in neurodegenerative diseases. Hsp70 family members are essential for preventing protein aggregation, refolding misfolded proteins, and targeting damaged proteins for degradation [1].
| Hsp70 Protein Family |
|---|
| Protein Name | Heat Shock 70 kDa Proteins (Hsp70) |
| Gene Symbols | HSPA1A, HSPA1B, HSPA2, HSPA5, HSPA8, HSPA9, HSPA14 |
| UniProt IDs | P0DMV8, P0DMV9, P54652, P11021, P11142, P38646, Q8WW36 |
| PDB IDs | 4KCM, 3FZF, 2E88, 4FSY, 5E84 |
| Molecular Weight | 65-71 kDa |
| Subcellular Localization | Cytoplasm, ER (BiP/GRP78), mitochondria, nucleus |
| Protein Family | Hsp70 family, Hsp70 superfamily |
| Brain Expression | Neurons, astrocytes, microglia, oligodendrocytes |
| Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [ALS](/diseases/als), [Huntington's Disease](/diseases/huntingtons) |
The Hsp70 family consists of multiple isoforms with distinct cellular localizations and functions. In the human genome, there are 13 Hsp70 family members, each with specific roles in cellular homeostasis [2]. The most well-studied members include:
- HSPA1A/Hsp70-1: Stress-inducible Hsp70, major heat shock protein
- HSPA1B/Hsp70-2: Highly similar to HSPA1A, co-expressed
- HSPA2/Hsp70-2: Testis-specific, involved in spermatogenesis
- HSPA5/GRP78/BiP: Endoplasmic reticulum resident, essential for ER function
- HSPA8/HSC70: Constitutively expressed, involved in autophagy
- HSPA9/GRP75/mtHsp75: Mitochondrial Hsp70, mitochondrial protein import
- HSPA14/LAP: Lysosome-associated Hsp70
Hsp70 proteins are ATP-dependent molecular chaperones that undergo large conformational changes during their functional cycle. They work in concert with co-chaperones from the Hsp40 (DnaJ) family and the Hsp70/Hsp90 organizing protein (HOP) to regulate their activity [3].
Hsp70 proteins have a characteristic two-domain architecture that enables their chaperone function:
¶ Domain Architecture
| Domain |
Residues |
Function |
| N-terminal ATPase domain |
~1-380 |
Binds and hydrolyzes ATP, regulates substrate binding |
| Substrate-binding domain (SBD) |
~400-500 |
Binds unfolded polypeptides |
| C-terminal lid |
~500-650 |
Covers SBD, completes substrate sequestration |
- ATPase domain: Belongs to the actin-Hsp70 superfamily, undergoes large conformational changes
- Lateral pore: Allows substrate entry into SBD
- Allosteric coupling: ATP hydrolysis in N-domain triggers conformational changes in C-domain
- EEVD motif: C-terminal sequence (EEVD) for co-chaperone binding
- Substrate-binding pocket: Hydrophobic residues recognizeunstructured protein regions
- ATP-bound state: Low substrate affinity, open conformation
- Substrate binding: Induces ATP hydrolysis
- ADP-bound state: High substrate affinity, closed conformation
- Nucleotide exchange: ADP release, ATP binding releases substrate
- Hsp40 (DnaJ): Delivers substrates, stimulates ATP hydrolysis
- HOP (Hsp70/Hsp90 Organizing Protein): Bridges Hsp70 and Hsp90
- BAG family: Nucleotide exchange factors
- Hsp110: Nucleotide exchange factors, holdases
| Function |
Description |
Mechanism |
| De novo folding |
Assists nascent protein folding |
Co-translational substrate binding |
| Refolding |
Rescues misfolded proteins |
ATP-dependent unfolding/refolding |
| Protein degradation |
Targets misfolded proteins to proteasome |
Cooperation with CHIP ubiquitin ligase |
| ** translocation** |
Imports proteins into ER/mitochondria |
Co-translational targeting |
| Disaggregation |
Solubilizes protein aggregates |
Cooperation with Hsp100/ClpB |
| Quality control |
Prevents aggregation |
Kinetic partitioning |
- Stress response: Rapidly induced by heat, oxidative stress, toxins
- Protein quality control: Surveys cellular protein homeostasis
- Signal transduction: Chaperones signaling proteins
- Transcription: Regulates steroid hormone receptors
- DNA replication: Involved in replication machinery
- Autophagy: HSC70 (HSPA8) involved in chaperone-mediated autophagy
In the central nervous system, Hsp70 family members serve specialized functions:
- Synaptic protein maintenance: Chaperones synaptic vesicles and receptors
- Axonal transport: Protects transport proteins
- Myelin maintenance: Supports oligodendrocyte function
- Neuroprotection: Reduces cellular stress
Hsp70 proteins are central to the pathogenesis of neurodegenerative diseases, which are characterized by protein misfolding and aggregation.
Hsp70 family members play complex roles in AD pathogenesis:
- Reduces Aβ toxicity: Hsp70 chaperones Aβ oligomers, reducing their toxicity [4]
- Modulates aggregation: Prevents Aβ fibril formation
- Enhances clearance: Cooperates with autophagy for Aβ clearance
- Cell surface Hsp70: Mediates Aβ internalization and degradation
- Tau binding: Directly interacts with hyperphosphorylated tau
- Prevents aggregation: Inhibits tau oligomerization
- Promotes degradation: Targets tau for proteasomal/autophagic clearance
- HSPA8 role: Critical in tau clearance pathways
- Hsp70 levels are reduced in AD brain
- Enhancing Hsp70 is protective in animal models
- Hsp70 inducers are in development
Hsp70 is particularly important in PD due to its role in alpha-synuclein clearance:
¶ Alpha-Synuclein Handling
- Direct interaction: Binds to α-synuclein aggregates [5]
- Prevents oligomerization: Inhibits toxic oligomer formation
- Promotes degradation: Targets α-syn for autophagic clearance
- Modulates aggregation: Redirects aggregation pathway
- Mitochondrial Hsp75 (HSPA9): Protects dopaminergic neurons
- Mitophagy: Essential for mitochondrial quality control
- Oxidative stress: Reduces ROS-induced damage
- LRRK2 chaperone: Hsp70 assists in LRRK2 folding
- Mutant LRRK2: May overwhelm chaperone systems
Hsp70 dysfunction contributes to motor neuron degeneration:
- Aggregate clearance: Insufficient to handle mutant protein aggregates
- Mutant SOD1: Hsp70 binds mutant SOD1 aggregates
- TDP-43 pathology: Hsp70 involved in TDP-43 clearance
- Therapeutic target: Enhancing Hsp70 is protective
Hsp70 plays important roles in huntingtin handling:
- Mutant huntingtin: Hsp70 modulates aggregation
- Transcriptional regulation: Assists mutant HTT function
- Axonal transport: Protects transport machinery
- Synaptic function: Maintains striatal synapse
- Tau clearance: Hsp70 promotes tau degradation
- FUS pathology: Hsp70 handles FUS aggregates
- TDP-43: Involved in TDP-43 clearance
Hsp70 operates in sophisticated protein quality control networks:
- Substrate recognition: Hydrophobic patch detection
- ATP-dependent cycling: Allosteric regulation
- Co-chaperone coordination: Hsp40 delivery, nucleotide exchange
- Handoff to degradation: CHIP-mediated ubiquitination
- Aggregate disassembly: Cooperation with Hsp100
Hsp70 interacts with multiple neuroprotective signaling pathways:
- NF-κB pathway: Hsp70 inhibits NF-κB activation
- JNK pathway: Hsp70 blocks pro-apoptotic JNK signaling
- p53 pathway: Modulates p53 function
- Heat shock factor 1 (HSF1): Hsp70 is HSF1 target, negative feedback
Hsp70 works with other chaperone systems:
- Hsp90 network: Cooperates in steroid receptor maturation
- Hsp60/Hsp10: Compartment-specific folding
- Proteasome: Directs substrates for degradation
- Autophagy: HSC70 in chaperone-mediated autophagy
Hsp70 activation represents a promising therapeutic strategy for neurodegenerative diseases:
| Approach |
Agent |
Status |
Mechanism |
| Hsp70 inducers |
Geldanamycin derivatives |
Preclinical |
HSF1 activation |
| Hsp90 inhibitors |
Geldanamycin, Radicicol |
Preclinical |
Hsp90 inhibition → Hsp70 induction |
| Small molecule activators |
YM-1, others |
Research |
Direct Hsp70 activation |
| Gene therapy |
AAV-Hsp70 |
Preclinical |
Overexpression |
Hsp90 inhibitors are particularly promising because they:
- Block Hsp90's anti-apoptotic function
- Release HSF1 to induce Hsp70
- Degrade mutant oncoproteins
- Sensitize cancer cells (dual benefit in some cases)
- BAG inhibitors: Block nucleotide exchange
- Hsp40 agonists: Enhance substrate delivery
- CHIP modulators: Affect ubiquitination rates
Several natural compounds induce Hsp70:
- Curcumin: Moderate Hsp70 induction
- Resveratrol: SIRT1-dependent effects
- Celastrol: Potent HSF1 activator
- Ginsenosides: Modest induction
Key experimental models for studying Hsp70:
- Hsp70 knockout mice: Viable but stress-sensitive
- Hsp70 transgenic mice: Protected from neurodegeneration
- HSF1 knockout mice: Compromised stress response
- AD models: Hsp70 overexpression reduces pathology
- PD models: Hsp70 protects dopaminergic neurons
- ALS models: Hsp70 delays disease progression
Hsp70 levels serve as biomarkers:
- Extracellular Hsp70 (eHsp70): Released under stress
- Hsp70 in CSF: Potential neurodegeneration marker
- Autoantibodies: Anti-Hsp70 in some diseases
- HSPA1A/HSPA1B polymorphisms: Linked to AD risk
- HSPA8 variants: Associated with PD
- HSPA9 mutations: Cause mitochondrial disease