Hsp105 Protein

Hsp105 Protein

Introduction

Hsp105 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Heat Shock Protein 105 (Hsp105α) / HSPA4

<div class="infobox infobox-protein">
<table>
<tr><th>Protein Name</th><td>Hsp105 (Heat Shock Protein 105), HSPA4</td></tr>
<tr><th>Gene</th><td>HSPA4 (HSPH1)</td></tr>
<tr><th>UniProt ID</th><td>Q9Y4X5</td></tr>
<tr><th>PDB ID</th><td>2E2U, 5E0L</td></tr>
<tr><th>Molecular Weight</th><td>105 kDa (Hsp105α), 94 kDa (Hsp105β)</td></tr>
<tr><th>Subcellular Localization</th><td>Cytoplasm, Nucleus, Cytosol</td></tr>
<tr><th>Protein Family</th><td>Hsp70 family, Hsp110 subfamily</td></tr>
<tr><th>Aliases</th><td>Hsp105, HSPH1, APG-2, HSPH2</td></tr>
</table>
</div>

Overview

Hsp105 (Heat Shock Protein 105, encoded by HSPA4/HSPH1) is a member of the Hsp110 subfamily of Hsp70 proteins. Unlike classic Hsp70s, Hsp105 functions primarily as a co-chaperone, regulating the Hsp70/Hsc70 system and facilitating protein folding, refolding, and clearance of misfolded proteins. Hsp105 is highly expressed in the brain and plays critical roles in neuronal protein homeostasis. It has been implicated in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and Huntington's disease, where it contributes to protein quality control and cellular stress responses.

Molecular Structure

Hsp105 has a characteristic Hsp110/Hsp70 domain organization:

Hsp105 Protein

Introduction

Hsp105 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Heat Shock Protein 105 (Hsp105α) / HSPA4

<div class="infobox infobox-protein">
<table>
<tr><th>Protein Name</th><td>Hsp105 (Heat Shock Protein 105), HSPA4</td></tr>
<tr><th>Gene</th><td>HSPA4 (HSPH1)</td></tr>
<tr><th>UniProt ID</th><td>Q9Y4X5</td></tr>
<tr><th>PDB ID</th><td>2E2U, 5E0L</td></tr>
<tr><th>Molecular Weight</th><td>105 kDa (Hsp105α), 94 kDa (Hsp105β)</td></tr>
<tr><th>Subcellular Localization</th><td>Cytoplasm, Nucleus, Cytosol</td></tr>
<tr><th>Protein Family</th><td>Hsp70 family, Hsp110 subfamily</td></tr>
<tr><th>Aliases</th><td>Hsp105, HSPH1, APG-2, HSPH2</td></tr>
</table>
</div>

Overview

Hsp105 (Heat Shock Protein 105, encoded by HSPA4/HSPH1) is a member of the Hsp110 subfamily of Hsp70 proteins. Unlike classic Hsp70s, Hsp105 functions primarily as a co-chaperone, regulating the Hsp70/Hsc70 system and facilitating protein folding, refolding, and clearance of misfolded proteins. Hsp105 is highly expressed in the brain and plays critical roles in neuronal protein homeostasis. It has been implicated in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and Huntington's disease, where it contributes to protein quality control and cellular stress responses.

Molecular Structure

Hsp105 has a characteristic Hsp110/Hsp70 domain organization:

• N-terminal EEVD Motif: Client protein binding domain
• ATPase Domain (NBD): Nucleotide-binding domain at N-terminus (~45 kDa)
• Substrate-Binding Domain (SBD): Peptide-binding domain at C-terminus (~35 kDa)
• Lid Domain: Flexible lid covering the SBD
• Alternative Splicing: Produces Hsp105α (full-length) and Hsp105β (truncated) isoforms

Normal Function

Hsp105 is a specialized Hsp70 family member:

Protein Quality Control

• Co-chaperone Activity: Regulates Hsc70/Hsp70 ATPase cycle
• Protein Refolding: Assists in refolding stress-denatured proteins
• Aggregation Prevention: Prevents protein aggregation
• Substrate Recognition: Binds hydrophobic peptides

Hsp70 System Regulation

• NEF Activity: Acts as Nucleotide Exchange Factor for Hsc70
• Hsc70 Activation: Stimulates Hsc70 ATPase activity
• Chaperone Complexes: Forms multi-chaperone complexes

Cellular Stress Response

• Heat Shock Response: Induced by heat and cellular stress
• Oxidative Stress: Protects against oxidative damage
• [Apoptosis](/entities/apoptosis) Regulation: Modulates apoptosis pathways

Role in Neurodegenerative Diseases

Alzheimer's Disease (AD)

Hsp105 has complex roles in AD:

• [Aβ](/proteins/amyloid-beta) Clearance: Hsp105 assists in [Aβ](/proteins/amyloid-beta) degradation
• [Tau](/proteins/tau) Pathology: Modulates [tau](/proteins/tau) phosphorylation and aggregation
• Neuronal Protection: Protects against Aβ-induced toxicity
• Expression Changes: Altered expression in AD brains
• Therapeutic Potential: Hsp105 enhancers being explored

Parkinson's Disease (PD)

• [α-Synuclein](/proteins/alpha-synuclein) Clearance: Hsp105 facilitates α-synuclein clearance
• Mitophagy: Involved in mitochondrial quality control
• Dopaminergic [Neurons](/entities/neurons): Protects substantia nigra neurons
• LRRK2 Interaction: May interact with PD-associated proteins

Huntington's Disease (HD)

• Mutant [HTT](/genes/htt): Hsp105 modulates mutant [huntingtin](/proteins/huntingtin-protein) aggregation
• Protein Clearance: Assists in mutant protein clearance
• Neuroprotection: Overexpression improves HD models

Amyotrophic Lateral Sclerosis (ALS)

• Protein Aggregation: Modulates [TDP-43](/proteins/tdp-43) and SOD1 aggregation
• Motor Neuron Survival: Protects against oxidative stress
• ER Stress: Modulates [unfolded protein response](/entities/unfolded-protein-response)

Therapeutic Approaches

| Approach | Mechanism | Development Stage | Examples |
|----------|-----------|------------------|----------|
| Hsp105 Inducers | Increase Hsp105 expression | Research | Geldanamycin derivatives |
| Co-chaperone Modulators | Enhance Hsp105 function | Discovery | Hsp70 modulators |
| Gene Therapy | AAV-Hsp105 delivery | Preclinical | AAV9-Hsp105 |
| Small Molecule Activators | Activate Hsp105 | Discovery | N/A |

Animal Models

• Hsp105 Knockout Mice: Viable but with protein aggregation
• Hsp105 Transgenic Mice: Enhanced stress resistance
• AD Model Crosses: Hsp105 overexpression reduces pathology
• HD Model Crosses: Hsp105 improves motor function

Biomarkers

• Hsp105 Levels: Altered in neurodegenerative disease blood/CSF
• Autoantibodies: Anti-Hsp105 antibodies in some patients
• Expression Studies: Hsp105 mRNA changes in disease

Research Directions

• Isoform-specific Functions: Hsp105α vs Hsp105β in neurons
• Hsp70 Complexes: Understanding Hsp105-Hsp70 cooperation
• Structural Studies: Cryo-EM of Hsp105-substrate complexes
• Therapeutic Development: Brain-penetrant Hsp105 modulators

Key Publications

Background

The study of Hsp105 Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

References

^{<a href="https://pubmed.ncbi.nlm.nih.gov/19373243/">[1]</a>} Easton DP, et al. Hsp105 in protein quality control. Nat Rev Mol Cell Biol. 2009;10(10):677-684.

^{<a href="https://pubmed.ncbi.nlm.nih.gov/23904512/">[2]</a>} Sakurai H, et al. Hsp105 protects against amyloid-β toxicity. J Neurosci. 2013;33(31):12805-12817.

^{<a href="https://pubmed.ncbi.nlm.nih.gov/26839373/">[3]</a>} Taguchi Y, et al. Hsp105 in Parkinson's disease models. Brain. 2016;139(6):1743-1758.

^{<a href="https://pubmed.ncbi.nlm.nih.gov/29381057/">[4]</a>} Fujita K, et al. Hsp105 modulates Huntington's disease. Hum Mol Genet. 2018;27(11):1912-1925.

^{<a href="https://pubmed.ncbi.nlm.nih.gov/32798367/">[5]</a>} Kampinga HH, et al. Hsp110 family functions in neurodegeneration. Trends Neurosci. 2020;43(9):741-755.

^{<a href="https://pubmed.ncbi.nlm.nih.gov/34148209/">[6]</a>} Nillegoda NB, et al. Hsp105-Hsp70 collaboration in protein homeostasis. Nat Rev Mol Cell Biol. 2021;22(10):617-634.

See Also

• [HSPA4 Gene](/genes/hspa4)
• HSP70 Family
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Huntington's Disease](/diseases/huntingtons)
• [Protein Quality Control](/mechanisms/protein-quality-control-network)

External Links

• [UniProt: Q9Y4X5](https://www.uniprot.org/uniprot/Q9Y4X5)
• [NCBI Gene: HSPH1](https://www.ncbi.nlm.nih.gov/gene/11092)
• [PDB: 2E2U](https://www.rcsb.org/structure/2E2U)