HSP90B1 — Heat Shock Protein 90 Beta Family Member 1

HSP90B1 — Heat Shock Protein 90 Beta Family Member 1

<div class="infobox infobox-gene">
| | |
|---|---| [@substrate2005]
| Gene Name | HSP90B1 | [@hspb2008]
| Full Name | Heat Shock Protein 90 Beta Family Member 1 | [@stress2007]
| Previous Symbols | GRP94, GP96 | [@hsp2008]
| Chromosomal Location | 12p12.3 | [@grp2012]
| UniProt ID | [P14625](https://www.uniprot.org/uniprot/P14625) | [@stress2009]
| Protein Family | Hsp90 family | [@hsp2009]
| Cellular Location | Endoplasmic reticulum lumen | [@grp2007]
| Molecular Weight | ~90 kDa | [@grp2012a]
</div>

Overview

HSP90B1 (Heat Shock Protein 90 Beta Family Member 1), also known as GRP94 (Glucose-Regulated Protein 94) or GP96, is a member of the Hsp90 family of molecular chaperones. Unlike its cytosolic counterpart HSP90AA1, HSP90B1 resides in the endoplasmic reticulum (ER) where it performs essential functions in protein folding, quality control, and calcium homeostasis [1](https://pubmed.ncbi.nlm.nih.gov/10644276/). HSP90B1 is a master regulator of ER proteostasis and plays critical roles in the cellular stress response relevant to neurodegenerative diseases.

Molecular Function

HSP90B1 is an ER-resident molecular chaperone with several unique features:

ER Localization Signal: HSP90B1 contains an N-terminal KDEL retrieval sequence that maintains its localization in the ER lumen. The protein is synthesized with a signal peptide that directs it to the ER secretory pathway [2](https://pubmed.ncbi.nlm.nih.gov/14744857/).

HSP90B1 — Heat Shock Protein 90 Beta Family Member 1

<div class="infobox infobox-gene">
| | |
|---|---| [@substrate2005]
| Gene Name | HSP90B1 | [@hspb2008]
| Full Name | Heat Shock Protein 90 Beta Family Member 1 | [@stress2007]
| Previous Symbols | GRP94, GP96 | [@hsp2008]
| Chromosomal Location | 12p12.3 | [@grp2012]
| UniProt ID | [P14625](https://www.uniprot.org/uniprot/P14625) | [@stress2009]
| Protein Family | Hsp90 family | [@hsp2009]
| Cellular Location | Endoplasmic reticulum lumen | [@grp2007]
| Molecular Weight | ~90 kDa | [@grp2012a]
</div>

Overview

HSP90B1 (Heat Shock Protein 90 Beta Family Member 1), also known as GRP94 (Glucose-Regulated Protein 94) or GP96, is a member of the Hsp90 family of molecular chaperones. Unlike its cytosolic counterpart HSP90AA1, HSP90B1 resides in the endoplasmic reticulum (ER) where it performs essential functions in protein folding, quality control, and calcium homeostasis [1](https://pubmed.ncbi.nlm.nih.gov/10644276/). HSP90B1 is a master regulator of ER proteostasis and plays critical roles in the cellular stress response relevant to neurodegenerative diseases.

Molecular Function

HSP90B1 is an ER-resident molecular chaperone with several unique features:

ER Localization Signal: HSP90B1 contains an N-terminal KDEL retrieval sequence that maintains its localization in the ER lumen. The protein is synthesized with a signal peptide that directs it to the ER secretory pathway [2](https://pubmed.ncbi.nlm.nih.gov/14744857/).

Substrate Recognition: HSP90B1 has a broad substrate repertoire, including nascent secretory and membrane proteins, immunoglobulin heavy chains, Toll-like receptors, and various disease-related proteins. The protein recognizes hydrophobic patches on partially folded proteins [3](https://pubmed.ncbi.nlm.nih.gov/15577934/).

Key Molecular Functions:

• Protein Folding: HSP90B1 assists in the folding and assembly of numerous client proteins, particularly those destined for secretion or membrane insertion.
• Quality Control: Misfolded proteins are retained in the ER and targeted for ER-associated degradation (ERAD) if folding cannot be achieved.
• Calcium Binding: HSP90B1 acts as a major calcium-binding protein in the ER, regulating calcium homeostasis.
• ER Stress Response: HSP90B1 is upregulated during ER stress and participates in the [unfolded protein response](/entities/unfolded-protein-response) (UPR).

Role in Neurodegeneration

Alzheimer's Disease

HSP90B1 plays complex roles in Alzheimer's disease pathogenesis:

[Amyloid Precursor Protein](/entities/app-protein) (APP) Processing: HSP90B1 interacts with APP and influences its processing by secretases. The chaperone activity of HSP90B1 affects whether APP is processed into [amyloid-beta](/proteins/amyloid-beta) or non-amyloidogenic fragments [4](https://pubmed.ncbi.nlm.nih.gov/18984547/).

ER Stress and the UPR: AD is associated with ER stress, and HSP90B1 is a key player in the UPR. Chronic activation of the UPR leads to neuronal [apoptosis](/entities/apoptosis), which may contribute to AD progression [5](https://pubmed.ncbi.nlm.nih.gov/17693355/).

[Tau](/proteins/tau) Pathology: HSP90B1 interacts with tau and influences its phosphorylation and aggregation. Some studies suggest Hsp90 inhibitors may have therapeutic potential by promoting tau clearance [6](https://pubmed.ncbi.nlm.nih.gov/18202190/).

Therapeutic Targeting: Hsp90 inhibitors have been investigated in AD models, with some showing promise in reducing amyloid-beta and tau pathology. However, the ER-resident HSP90B1 may have different effects compared to cytosolic Hsp90.

Parkinson's Disease

In Parkinson's disease, HSP90B1 has several relevant functions:

[Alpha-Synuclein](/proteins/alpha-synuclein) Handling: HSP90B1 can interact with alpha-synuclein and influence its folding and aggregation. The ER chaperone may help target misfolded alpha-synuclein for degradation [7](https://pubmed.ncbi.nlm.nih.gov/22472578/).

ER Stress in Dopaminergic [Neurons](/entities/neurons): Dopaminergic neurons are particularly vulnerable to ER stress, and HSP90B1 upregulation is observed in PD brain tissue. This may represent a protective response that becomes insufficient with disease progression [8](https://pubmed.ncbi.nlm.nih.gov/19149626/).

LRRK2 Processing: HSP90B1 interacts with LRRK2, the most common genetic cause of familial PD. The chaperone helps properly fold mutant LRRK2, and Hsp90 inhibitors can accelerate mutant LRRK2 degradation [9](https://pubmed.ncbi.nlm.nih.gov/19543268/).

Amyotrophic Lateral Sclerosis

HSP90B1 is implicated in ALS through several mechanisms:

SOD1 Mutants: HSP90B1 interacts with mutant SOD1 and helps retain misfolded SOD1 in the ER. This retention may contribute to ER stress and motor neuron dysfunction [10](https://pubmed.ncbi.nlm.nih.gov/17572753/).

ER Stress Response: The UPR is chronically activated in ALS, and HSP90B1 plays a key role in this response. Dysregulation of the ER stress response may contribute to motor neuron death.

[TDP-43](/mechanisms/tdp-43-proteinopathy) Pathology: HSP90B1 may interact with TDP-43, which forms cytoplasmic inclusions in most ALS cases. The chaperone system may be overwhelmed in disease.

Huntington's Disease

HSP90B1 has been investigated in Huntington's disease:

Mutant Huntingtin Handling: HSP90B1 interacts with mutant [huntingtin protein](/proteins/huntingtin) and influences its aggregation. The ER chaperone may help target mutant huntingtin for degradation [11](https://pubmed.ncbi.nlm.nih.gov/20458336/).

ER Calcium Dysregulation: HSP90B1's calcium-binding function is relevant to HD, where calcium signaling is disrupted. Maintaining proper calcium homeostasis may be protective.

Expression Patterns

HSP90B1 is expressed in most cell types, with highest expression in cells with high secretory activity, including plasma cells, pancreatic acinar cells, and hepatocytes. In the nervous system, HSP90B1 is expressed in neurons and glial cells throughout the brain and spinal cord. Expression is strongly induced by ER stress, glucose deprivation, and other cellular stresses.

Therapeutic Implications

HSP90B1 is a therapeutic target for neurodegeneration:

Hsp90 Inhibitors: While most Hsp90 inhibitors target cytosolic Hsp90, ER-selective inhibitors are being developed to specifically target HSP90B1.

Enhancing Chaperone Activity: Compounds that enhance HSP90B1 function could improve ER proteostasis and protect neurons.

Modulating UPR Signaling: Targeting the UPR through HSP90B1 modulation may help restore cellular homeostasis.

Calcium Homeostasis: Maintaining proper calcium handling through HSP90B1 modulation may be beneficial in diseases like HD.

See Also

• [Heat Shock Protein 90 Family](/proteins/hsp90-family)
• [Endoplasmic Reticulum Stress](/mechanisms/er-stress-unfolded-protein-response)
• [Protein Quality Control](/mechanisms/protein-quality-control-ubiquitin-proteasome)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [Huntington's Disease](/diseases/huntington-disease)

References