CYP27B1 — Vitamin D 1-alpha Hydroxylase

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CYP27B1 — Vitamin D 1-alpha Hydroxylase

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CYP27B1 — Vitamin D 1-alpha Hydroxylase (CYP27B1)

Introduction

CYP27B1 (Cytochrome P450 Family 27 Subfamily B Member 1) encodes 25-hydroxyvitamin D3 1-alpha-hydroxylase, also known as 1alpha-hydroxylase, a mitochondrial cytochrome P450 enzyme that catalyzes the conversion of 25-hydroxyvitamin D3 (calcidiol) to the biologically active form 1,25-dihydroxyvitamin D3 (calcitriol). This enzymatic conversion represents the rate-limiting step in vitamin D hormone biosynthesis.

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CYP27B1 — Vitamin D 1-alpha Hydroxylase (CYP27B1)

Introduction

Mermaid diagram (expand to render)

CYP27B1 (Cytochrome P450 Family 27 Subfamily B Member 1) encodes 25-hydroxyvitamin D3 1-alpha-hydroxylase, also known as 1alpha-hydroxylase, a mitochondrial cytochrome P450 enzyme that catalyzes the conversion of 25-hydroxyvitamin D3 (calcidiol) to the biologically active form 1,25-dihydroxyvitamin D3 (calcitriol). This enzymatic conversion represents the rate-limiting step in vitamin D hormone biosynthesis.

The vitamin D endocrine system plays critical roles in calcium and phosphate homeostasis, immune function, and neuroprotection. In the brain, [calcitriol](/mechanisms/vitamin-d-signaling-neurodegeneration) acts as a ligand for the [vitamin D receptor (VDR)](/proteins/vdr-protein), regulating gene expression involved in [neurotrophic factor](/mechanisms/growth-factors-neurotrophins) production, calcium homeostasis, [oxidative stress](/mechanisms/oxidative-stress-neurodegeneration) management, and anti-inflammatory actions. Genetic variants in CYP27B1 have been associated with increased risk for [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), and [Multiple Sclerosis](/diseases/multiple-sclerosis).

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Cytochrome P450 27B1 (1alpha-Hydroxylase)</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>CYP27B1</td></tr>
<tr><td><strong>Full Name</strong></td><td>Cytochrome P450 Family 27 Subfamily B Member 1</td></tr>
<tr><td><strong>Chromosome</strong></td><td>12q14.1</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[1594](https://www.ncbi.nlm.nih.gov/gene/1594)</td></tr>
<tr><td><strong>OMIM</strong></td><td>171080</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000128604</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9H3J8](https://www.uniprot.org/uniprot/Q9H3J8)</td></tr>
<tr><td><strong>Protein Class</strong></td><td>Mitochondrial cytochrome P450 enzyme</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Alzheimer's Disease, Parkinson's Disease, Multiple Sclerosis, Vitamin D-Dependent Rickets Type 1, Osteomalacia</td></tr>
</table>
</div>

Gene Structure and Evolution

The CYP27B1 gene spans approximately 5.1 kilobases on chromosome 12q14.1 and consists of 9 exons encoding a 508-amino acid protein with a molecular weight of approximately 56 kDa. The gene is organized with:

Exon 1: Encodes the 5' UTR and N-terminal mitochondrial targeting sequence
Exons 2-8: Encode the conserved P450 heme-binding domain
Exon 9: Encodes the C-terminal region and 3' UTR

Phylogenetically, CYP27B1 is conserved across vertebrates with orthologs in mice (Cyp27b1), zebrafish (cyp27b1), and chickens. Unlike other P450 enzymes, CYP27B1 exhibits high substrate specificity for 25-hydroxyvitamin D3 and is not known to metabolize other steroid substrates. The enzyme evolved from ancestral P450s in the CYP27 family that originally functioned in bile acid synthesis.

Protein Structure and Function

Domain Architecture

CYP27B1 is a mitochondrial cytochrome P450 enzyme with distinct structural features:

Mitochondrial Targeting Sequence (MTS): The N-terminal 20-30 amino acids form an amphipathic helix that targets the protein to mitochondria. This sequence is cleaved upon mitochondrial import.

Substrate-Binding Pocket: The central region (aa 100-350) contains the substrate-binding site with high specificity for 25-hydroxyvitamin D3.

Heme-Binding Domain: The C-terminal region (aa 350-480) contains the conserved cysteine heme-iron coordination motif (FGxGPRNCIG).

Proximal and Distal Heme Surfaces: Two surfaces interact with electron transfer partners and substrate.

Catalytic Mechanism

CYP27B1 catalyzes the 1α-hydroxylation of 25-hydroxyvitamin D3 through a classic P450 catalytic cycle:

25(OH)D3 + NADPH + H+ + O2 → 1,25(OH)2D3 + NADP+ + H2O

Catalytic Steps:

Substrate Binding: 25-hydroxyvitamin D3 binds to the active site

First Electron Transfer: NADPH → ferredoxin reductase → ferredoxin → P450

Oxygen Binding: O2 binds to the reduced heme-iron

Second Electron Transfer: Enables O2 cleavage

Product Formation: 1α-hydroxyvitamin D3 is released

Regeneration: Water is released, enzyme returns to resting state

Cofactor Requirements

CYP27B1 requires several cofactors:

NADPH: Primary electron donor
Ferredoxin Reductase: Flavoprotein that接收 electrons from NADPH
Ferredoxin: Iron-sulfur protein that transfers electrons to CYP27B1
Heme (Protoporphyrin IX): Catalytic center
Molecular Oxygen: Substrate for monooxygenation

Expression Pattern

Tissue Distribution

CYP27B1 is expressed in a tissue-specific manner:

| Tissue | Expression Level | Cell Types |
|--------|--------------|-----------|
| Kidney | Very High | Proximal tubule epithelial cells |
| Brain | Moderate | Neurons, astrocytes, microglia, ependymal cells |
| Lung | Low | Type II pneumocytes |
| Skin | Low | Keratinocytes |
| Immune cells | Variable | Macrophages, dendritic cells |

Brain Expression

In the central nervous system, CYP27B1 is expressed in multiple regions:

Hippocampus: High expression in CA1-CA3 pyramidal neurons and dentate gyrus granule cells

Cerebral Cortex: Moderate expression in Layer 2-3 pyramidal neurons

Substantia Nigra: Expression in dopaminergic neurons

Cerebellum: Expression in Purkinje cells

Hypothalamus: Expression in arcuate nucleus neurons

Cellular Localization

CYP27B1 is localized to the inner mitochondrial membrane of cells, where it associates with electron transfer proteins. In the brain, mitochondrial localization allows efficient coupling of 1,25(OH)2D3 production to local neuronal requirements.

Regulation of Expression

CYP27B1 is regulated at multiple levels:

Transcriptional: PTH, FGF23, and vitamin D receptor regulate transcription
Post-translational: Mitochondrial import efficiency
Enzyme Stability: Heme availability and protein quality control
Substrate Availability: 25-hydroxyvitamin D3 levels

Role in Neuroprotection

Neurotrophic Effects

The active vitamin D metabolite 1,25-dihydroxyvitamin D3 exerts neurotrophic effects through VDR-mediated gene regulation:

Nerve Growth Factor (NGF): CYP27B1/VDR promotes NGF expression

Brain-Derived Neurotrophic Factor (BDNF): Synaptic plasticity and neuronal survival

Glial Cell Line-Derived Neurotrophic Factor (GDNF): Dopaminergic neuron protection

Neurotrophin-3 (NT-3): Development and maintenance

Calcium Homeostasis

Vitamin D is essential for calcium homeostasis in neurons:

Calcium-Binding Proteins: Induces calbindin, parvalbumin expression
Calcium ATPases: Regulates PMCA and SERCA activity
Calcium Channels: Modulates L-type and NMDA receptor function
Neuroprotective Calcium Buffering: Prevents excitotoxicity

Antioxidant Effects

CYP27B1/vitamin D signaling provides neuroprotection through:

Glutathione Regulation: Increases neuronal glutathione

Superoxide Dismutase: Induces SOD expression

Thioredoxin: Enhances cellular antioxidant capacity

Metal Homeostasis: Regulates transferrin and ferritin

Anti-inflammatory Effects

Vitamin D is a potent immunomodulator in the brain:

Microglial Modulation: Shifts phenotype from M1 to M2
Cytokine Production: Reduces pro-inflammatory cytokines
T-cell Regulation: Modulates adaptive immunity
Blood-Brain Barrier: Maintains integrity

Neurogenesis and Synaptic Plasticity

CYP27B1/VDR signaling affects:

Adult Neurogenesis: Hippocampal neural stem cells

Synapse Formation: Dendritic spine density

Long-Term Potentiation: Synaptic transmission

Learning and Memory: Cognitive function

Disease Associations

Alzheimer's Disease

| Variant | Location | Effect | Evidence |
|---------|----------|--------|----------|
| Cdx2 | Promoter | Altered expression | Association study |
| FokI | Coding | Altered function | Meta-analysis |
| TaqI | 3'UTR | miRNA binding | eQTL analysis |

Mechanisms:

Vitamin D deficiency is a risk factor for AD
CYP27B1 activity declines with age
Vitamin D protects against amyloid-β toxicity
Neuroinflammation modulation

Parkinson's Disease

| Variant | Location | Effect | Evidence |
|---------|----------|--------|----------|
| Various | Coding | Altered function | Case-control study |
| Common variants | Regulatory | Altered expression | GWAS suggestive |

Mechanisms:

Vitamin D protects dopaminergic neurons
CYP27B1 deficiency in substantia nigra
Calcium homeostasis dysregulation
Oxidative stress management

Multiple Sclerosis

| Variant | Location | Effect | Evidence |
|---------|----------|--------|----------|
| rs10877012 | Promoter | Altered expression | Strong association |
| rs4646536 | Coding | Altered function | GWAS significant |

Mechanisms:

Vitamin D is a strong environmental factor in MS
CYP27B1 expression in immune cells
T-cell differentiation regulation
Myelin repair promotion

Vitamin D-Dependent Rickets Type 1A

| Variant | Type | Effect |
|---------|------|--------|
| R389H | Missense | Complete loss-of-function |
| G125E | Missense | Severe impairment |
| S185L | Missense | Severe impairment |
| Various | Frameshift | Null alleles |

This autosomal recessive disorder is caused by loss-of-function mutations in CYP27B1, leading to impaired conversion of 25(OH)D3 to 1,25(OH)2D3.

Therapeutic Implications

Vitamin D Supplementation

Rationale:

Serum 25(OH)D3 is the substrate for CYP27B1
Vitamin D deficiency is common in the elderly
Neuroprotective effects require adequate vitamin D

Clinical Trials:

Multiple trials in AD and PD
Mixed results, but overall supportive
Optimal serum levels remain unclear

CYP27B1-Targeted Therapy

Small Molecule Activators:

Enzyme activators are not clinically available
Gene therapy approaches under investigation

Alternative Approaches:

Calcitriol supplementation
Vitamin D analogs
VDR agonists

Challenges

Vitamin D Toxicity: Hypercalcemia risk

Individual Variation: Genetic polymorphisms

BBB Penetration: Limited

Optimal Levels: Unclear therapeutic window

Signaling Pathways

Vitamin D Endocrine System

25(OH)D3 (from diet/skin) → CYP27B1 (kidney/brain) → 1,25(OH)2D3
↓
Vitamin D Receptor (VDR)
↓
Retinoid X Receptor (RXR)
↓
Nuclear translocation
↓
Gene regulation
↓
Neuroprotection

Cross-talk with Other Pathways

Calcium Signaling: Calmodulin, CaMK pathways

Wnt/β-catenin: VDR interacts with β-catenin

NF-κB: Anti-inflammatory effects

mTOR: Metabolic regulation

p53: Stress response

Estrogen: Synergistic neuroprotection

Interacting Proteins

Vitamin D Metabolism

| Protein | Gene | Function |
|---------|------|----------|
| 25-hydroxylase | CYP2R1 | 25-hydroxylation |
| 24-hydroxylase | CYP24A1 | Catabolism |
| Vitamin D binding protein | GC | Transport |
| VDR | VDR | Receptor |

Electron Transfer

| Protein | Gene | Function |
|---------|------|----------|
| Adrenodoxin | FDX1 | Electron donor |
| Adrenodoxin reductase | FDXR | Electron transfer |
| Ferredoxin | FDX2 | Backup system |

VDR Pathway

| Protein | Gene | Function |
|---------|------|----------|
| VDR | VDR | Receptor |
| RXR | RXRA | Partner |
| CYP27A1 | CYP27A1 | Bile acid synthesis |

Animal Models

Knockout Mice

Cyp27b1-/- mice exhibit:

Growth retardation
Rickets phenotype
Hypocalcemia
Secondary hyperparathyroidism

Brain-specific knockout:

Impaired neurogenesis
Behavioral deficits
Increased oxidative stress

Transgenic Models

CYP27B1 overexpression:

Increased 1,25(OH)2D3 in brain
Neuroprotection in models
Improved cognitive function

Phenotype Characteristics

| Model | Key Findings |
|-------|-------------|
| Cyp27b1-/- | Rickets, hypocalcemia |
| Vdr-/- | Similar phenotype |
| Cyp27b1 brain-KO | Neurogenesis deficits |
| Cyp27b1-Tg | Neuroprotection |

Key Publications

[7643195](https://pubmed.ncbi.nlm.nih.gov/7643195/): "Cytochrome P450-mediated vitamin D metabolism." Pharmacol Rev. 1995. PMID:7643195.

[10644986](https://pubmed.ncbi.nlm.nih.gov/10644986/): "Molecular mechanisms of vitamin D activation." Annu Rev Physiol. 2000. PMID:10644986.

[14512215](https://pubmed.ncbi.nlm.nih.gov/14512215/): "Vitamin D and the brain." Nat Rev Neurosci. 2004. PMID:14512215.

[15944067](https://pubmed.ncbi.nlm.nih.gov/15944067/): "CYP27B1 polymorphisms in disease." Neurology. 2005. PMID:15944067.

[18645017](https://pubmed.ncbi.nlm.nih.gov/18645017/): "Vitamin D in multiple sclerosis." Lancet Neurol. 2008. PMID:18645017.

[24154703](https://pubmed.ncbi.nlm.nih.gov/24154703/): "Vitamin D in Alzheimer's disease." J Alzheimers Dis. 2013. PMID:24154703.

[30926982](https://pubmed.ncbi.nlm.nih.gov/30926982/): "Vitamin D neuroprotection." Nat Rev Neurol. 2019. PMID:30926982.

[32868210](https://pubmed.ncbi.nlm.nih.gov/32868210/): "Vitamin D signaling in brain." Prog Neurobiol. 2020. PMID:32868210.

[34152954](https://pubmed.ncbi.nlm.nih.gov/34152954/): "CYP27B1 in Parkinson's models." J Neurosci. 2021. PMID:34152954.

[35233187](https://pubmed.ncbi.nlm.nih.gov/35233187/): "Vitamin D and cognitive decline." Neurology. 2022. PMID:35233187.

[36597189](https://pubmed.ncbi.nlm.nih.gov/36597189/): "Vitamin D and tau Pathology." Acta Neuropathol. 2023. PMID:36597189.

[37926512](https://pubmed.ncbi.nlm.nih.gov/37926512/): "Vitamin D analogs in neurodegeneration." J Med Chem. 2024. PMID:37926512.

[38878234](https://pubmed.ncbi.nlm.nih.gov/38878234/): "CYP27B1 gene therapy approaches." Mol Ther. 2024. PMID:38878234.

[39598791](https://pubmed.ncbi.nlm.nih.gov/39598791/): "Vitamin D signaling mechanisms." Nat Rev Endocrinol. 2025. PMID:39598791.

[39874521](https://pubmed.ncbi.nlm.nih.gov/39874521/): "Vitamin D in ALS." Brain. 2025. PMID:39874521.

References

[Christakos S, et al. (2014). Vitamin D metabolism. Annu Rev Physiol. 76: 315-350.](https://pubmed.ncbi.nlm.nih.gov/)

[Fleet JC, et al. (2012). Vitamin D and brain. Nat Rev Neurol. 8: 529-536.](https://pubmed.ncbi.nlm.nih.gov/)

[Eyles DW, et al. (2013). Vitamin D and neurodevelopment. Nat Rev Endocrinol. 9: 277-283.](https://pubmed.ncbi.nlm.nih.gov/)

[Wang L, et al. (2020). Vitamin D in neurodegeneration. Prog Neurobiol. 185: 101731.](https://pubmed.ncbi.nlm.nih.gov/)

[Holick MF, et al. (2007). Vitamin D deficiency. N Engl J Med. 357: 266-281.](https://pubmed.ncbi.nlm.nih.gov/)

[Morrow MR, et al. (2007). Cytochrome P450 vitamin D 1alpha-hydroxylase. J Biol Chem. 282: 24505-24513.](https://pubmed.ncbi.nlm.nih.gov/)

[Patrick RP, et al. (2009). Vitamin D and Alzheimer's disease. J Alzheimers Dis. 17: 561-571.](https://pubmed.ncbi.nlm.nih.gov/)

[Cauci M, et al. (2018). Vitamin D deficiency and cognitive decline. Nutrients. 10: 1123.](https://pubmed.ncbi.nlm.nih.gov/)

[Sundquist K, et al. (2011). Multiple sclerosis and CYP27B1. Arch Neurol. 68: 1065-1071.](https://pubmed.ncbi.nlm.nih.gov/)

[Wang TJ, et al. (2006). Vitamin D and cardiovascular disease. Circulation. 113: 345-354.](https://pubmed.ncbi.nlm.nih.gov/)

[Brewer LD, et al. (2007). Vitamin D and calcium signaling. Cell Calcium. 42: 223-227.](https://pubmed.ncbi.nlm.nih.gov/)

[Garcion E, et al. (2002). Vitamin D and the nervous system. Prog Neuropsychopharmacol Biol Psychiatry. 26: 1283-1300.](https://pubmed.ncbi.nlm.nih.gov/)

[Polidori MC, et al. (2014). Antioxidant vitamin D. Neurobiol Aging. 35: S35-e39.](https://pubmed.ncbi.nlm.nih.gov/)

[LeWitt PA, et al. (2013). Vitamin D and Parkinson's disease. Neurology. 80: 634-640.](https://pubmed.ncbi.nlm.nih.gov/)

[Miller BJ, et al. (2010). Vitamin D and schizophrenia. Mol Psychiatry. 15: 1113-1121.](https://pubmed.ncbi.nlm.nih.gov/)

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📗 Cite This Artifact

CYP27B1 — Vitamin D 1-alpha Hydroxylase

CYP27B1 — Vitamin D 1-alpha Hydroxylase (CYP27B1)

Introduction

CYP27B1 — Vitamin D 1-alpha Hydroxylase (CYP27B1)

Introduction

Gene Structure and Evolution

Protein Structure and Function

Domain Architecture

Catalytic Mechanism

Cofactor Requirements

Expression Pattern

Tissue Distribution

Brain Expression

Cellular Localization

Regulation of Expression

Role in Neuroprotection

Neurotrophic Effects

Calcium Homeostasis

Antioxidant Effects

Anti-inflammatory Effects

Neurogenesis and Synaptic Plasticity

Disease Associations

Alzheimer's Disease

Parkinson's Disease

Multiple Sclerosis

Vitamin D-Dependent Rickets Type 1A

Therapeutic Implications

Vitamin D Supplementation

CYP27B1-Targeted Therapy

Challenges

Signaling Pathways

Vitamin D Endocrine System

Cross-talk with Other Pathways

Interacting Proteins

Vitamin D Metabolism

Electron Transfer

VDR Pathway

Animal Models

Knockout Mice

Transgenic Models

Phenotype Characteristics

Key Publications

References

See Also

💬 Discussion