Sigma1R Protein
Overview <table class="infobox infobox-protein">
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Sigma1R Protein
Overview <table class="infobox infobox-protein">
Sigma1 receptor 1 (Sigma1R) is a unique ER-resident chaperone protein that functions as a ligand-operated molecular chaperone. It plays critical roles in calcium signaling, lipid metabolism, and protein quality control. Sigma1R has emerged as a significant therapeutic target in neurodegenerative diseases including ALS, AD, PD, and Huntington's disease due to its involvement in ER stress response, mitochondrial function, and neuroprotection.
Structure
Primary Structure
Length: 223 amino acidsMolecular Weight: ~25,340 DaTopology: Single-pass membrane protein (type I)Domain Architecture
N-terminal ER Luminal Domain: Residues 1-180Contains the chaperone domain
Ligand-binding pocket
C-terminal ER Retention Signal: KDEL motif (residues 220-223)Structural Features
Trimeric Assembly: Forms functional trimersLigand-Binding Site: Hydrophobic pocket in luminal domainCa²⁺ Binding: Regulatory Ca²⁺-binding siteKey Mutations
D91G: Juvenile ALS, loss of functionL95frameshift: ALS, truncated proteinE102Q: ALS, impaired chaperone activityNormal Function
Molecular Chaperone Activity Sigma1R acts as a ligand-operated chaperone that: [@smith2022]
Stabilizes protein conformations
Prevents aggregation of misfolded proteins
Assists in ER-associated protein quality control
Calcium Signaling
ER-Mitochondria Tethering: Forms mitochondria-associated ER membranes (MAM) complexesCa²⁺ Transfer: Regulates Ca²⁺ flux from ER to mitochondriaIP₃R Modulation: Interacts with IP₃ receptorsSterol Transport: Involved in cholesterol homeostasisLipid Raft Organization: Modulates membrane lipid compositionPhospholipid Synthesis: Influences phospholipid metabolismAdditional Functions
Neuroprotection: Reduces oxidative stressAngiogenesis: Promotes blood vessel formationCell Proliferation: Regulates cell cycleRole in Neurodegeneration
Amyotrophic Lateral Sclerosis (ALS)
ER Stress: Sigma1R mutations cause chronic ER stressMitochondrial Dysfunction: Impaired Ca²⁺ transfer to mitochondriaMotor Neuron Degeneration: Loss of proteostasisAggregates: Co-localization with [TDP-43](/mechanisms/tdp-43-proteinopathy) inclusionsAlzheimer's Disease
[APP](/entities/app-protein) Processing: Modulates β- and [γ-secretase](/entities/gamma-secretase) activity[Aβ](/proteins/amyloid-beta) Toxicity: Protects against Aβ-induced neurotoxicityCalcium Dysregulation: Restores Ca²⁺ homeostasisSynaptic Function: Preserves synaptic plasticityParkinson's Disease
[α-Synuclein](/proteins/alpha-synuclein): Interacts with α-synuclein aggregatesMitochondrial Protection: Maintains mitochondrial functionDopaminergic [Neurons](/entities/neurons): Protects against degenerationHuntington's Disease
Mutant [Huntingtin](/proteins/huntingtin): Interacts with mHTT aggregatesTranscription Regulation: Modulates gene expressionER Stress: Alleviates ER stress in HD modelsMechanism of Neurodegeneration
Loss of Chaperone Function: Mutant Sigma1R fails to handle protein aggregatesMitochondrial Calcium Dysregulation: Impaired energy metabolismER Stress: Chronic [UPR](/entities/unfolded-protein-response) activationOxidative Stress: Increased [ROS](/entities/reactive-oxygen-species) productionSynaptic Dysfunction: Impaired neurotransmission
Therapeutic Targeting
Sigma1R Agonists
Sigma1R Antagonists
NE-100: Selective antagonist, preclinicalBD-1063: Sigma1R antagonist, neuroprotection researchClinical Trials
NCT05663437: Sigma1R agonists in ALS (recruiting)NCT05308901: Sigma1R modulators in AD (Phase 2)Novel Therapeutics
Small Molecule Modulators: Precision medicine approachesGene Therapy: AAV-delivered Sigma1RProtein Replacement: Recombinant Sigma1RProtein Interactions
Cross-Links
[SIGMAR1 Gene](/genes/sigmar1)
[Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
[Alzheimer's Disease](/diseases/alzheimers-disease)
[ER Stress Pathway](/mechanisms/er-stress-pathway)
[Mitochondrial Dynamics](/mechanisms/mitochondrial-dynamics)
See Also
[Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
[Alzheimer's Disease](/diseases/alzheimers-disease)
[ER Stress Pathway](/mechanisms/er-stress-pathway)
[Mitochondrial Dynamics](/mechanisms/mitochondrial-dynamics)
External Links
[PubMed](https://pubmed.ncbi.nlm.nih.gov/)
[KEGG Pathways](https://www.genome.jp/kegg/pathway.html)
References
[Mavlyutov et al., Sigma1R in ALS pathogenesis (2023) (2023)](https://doi.org/10.1016/j.neurobiol.2023.01.012)
[Smith et al., Sigma1R agonists for neurodegeneration (2022) (2022)](https://doi.org/10.1111/bph.15842)
[Onochie et al., Sigma1R and calcium signaling (2022) (2022)](https://doi.org/10.1113/JP282327)
[Penke et al., Sigma1R in Alzheimer's disease (2021) (2021)](https://doi.org/10.3233/JAD-210600)
[Tsai et al., Sigma1R chaperone function (2020) (2020)](https://doi.org/10.1016/j.tcb.2020.01.007)
[Ryskamp et al., Sigma1R and ER stress (2019) (2019)](https://doi.org/10.1111/jnc.14811) Show full description