:: infobox .infobox-protein
| ADARB1 Protein (Adenosine Deaminase Acting on RNA 1) |
|
| Gene |
ADARB1 |
| UniProt |
P78563 |
| Molecular Weight |
~70 kDa |
| Length |
739 amino acids |
| Subcellular Localization |
Nucleus (nucleolus) |
| Protein Family |
ADAR family |
| Aliases |
ADAR2, RED1, ADARL1 |
| Enzymatic Activity |
A-to-I RNA editing |
===
ADARB1 (Adenosine Deaminase Acting on RNA 1), also known as ADAR2, is a dsRNA-specific adenosine deaminase that catalyzes the deamination of adenosine to inosine (A-to-I editing) in double-stranded RNA (dsRNA) substrates. This post-transcriptional modification is essential for neurological development and function, affecting RNA splicing, miRNA processing, and receptor function. ADARB1 dysregulation has been implicated in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS), and various cancers.
ADARB1 is a 739-amino acid protein with a molecular weight of approximately 70 kDa. The protein contains several functional domains:
- N-terminal double-strand RNA binding domains (dsRBDs): Three dsRBDs (dsRBD1, dsRBD2, dsRBD3) recognize and bind to dsRNA substrates with high affinity
- C-terminal catalytic deaminase domain: Contains the zinc-binding motif (HXEXnH) essential for catalytic activity
- Nuclear localization signal (NLS): Directs protein to the nucleus
- Nucleolar targeting domain: ADARB1 localizes to the nucleolus where it processes some substrates
The deaminase domain contains the conserved His-Glu-X-Leu-His sequence that coordinates zinc ion (Zn²⁺) essential for catalytic function. The dsRBDs provide substrate specificity and are essential for recognizing editing sites in precursor mRNA (pre-mRNA).
ADARB1 catalyzes A-to-I editing through a hydrolytic deamination reaction:
Adenosine + H₂O → Inosine + NH₃
The reaction mechanism involves:
- Substrate binding: dsRBDs recognize the editing site in pre-mRNA
- Zinc-mediated catalysis: Zn²⁺ coordinates water for nucleophilic attack
- Proton transfer: His residues facilitate proton transfer
- Product release: Inosine-containing RNA is released
¶ Neurological Development and Function
ADARB1 plays critical roles in brain development and neuronal function:
- GluR2 Q/R site editing: Essential editing of the AMPA receptor GluR2 (GRIA2) subunit at the Q/R site. Unedited GluR2 permits Ca²⁺ influx, leading to excitotoxicity
- 5-HT2C receptor editing: Regulates serotonin 5-HT2C receptor editing at multiple sites, modulating G-protein signaling
- MiRNA processing: Edits miRNA precursors, affecting miRNA maturation and target specificity
- Retrotransposon editing: Targets ALU repeats and other endogenous retrotransposons, suppressing aberrant RNA processing
- mRNA splicing: A-to-I editing can alter splice site selection
ADARB1 contributes to circadian clock function through A-to-I editing of clock gene transcripts, regulating RNA rhythm and maintaining circadian homeostasis.
ADARB1 activity is significantly altered in AD brain:
- Globally reduced editing: ADARB1-mediated editing is decreased in AD temporal cortex and hippocampus
- Target genes affected: Editing of GluR2, 5-HT2C, and other neuronal transcripts is reduced
- Mechanism links: Aβ accumulation may directly or indirectly suppress ADARB1 activity
- Therapeutic potential: Restoring ADARB1 activity could ameliorate synaptic dysfunction
ADARB1 alterations in PD include:
- Blood-derived network: ADARB1-centered gene networks are dysregulated in PD blood cells
- Lewy body pathology: A-to-I editing alterations may contribute to alpha-synuclein aggregation
- Mitochondrial dysfunction: ADARB1 may affect RNA editing of mitochondrial-related transcripts
- Therapeutic targeting: Enhancing RNA editing is being explored
ADARB1 deficiency contributes to ALS pathogenesis:
- Reduced GluR2 editing: Compromised Q/R site editing increases Ca²⁺ permeability through AMPA receptors
- Motor neuron excitotoxicity: Unedited GluR2 leads to excessive calcium influx and excitotoxic cell death
- Altered RNA processing: Global RNA processing defects in motor neurons
- Therapeutic approaches: Gene therapy to restore ADARB1 function is under investigation
Biallelic ADARB1 variants cause Aicardi-Goutières syndrome (AGS), a severe neurodevelopmental disorder characterized by:
- Microcephaly
- Intellectual disability
- Seizures
- Cerebral atrophy
This confirms ADARB1's essential role in brain development.
ADARB1 interacts with and is regulated by:
| Partner |
Interaction Type |
Functional Consequence |
| GRIA2 (GluR2) |
Substrate |
Q/R site editing |
| HTR2C (5-HT2C) |
Substrate |
Multiple site editing |
| DICER1 |
Complex |
miRNA processing |
| ADAR |
Homolog |
Redundant editing |
| Importin α/β |
Transport |
Nuclear import |
| PIWIL3 |
Complex |
piRNA processing |
ADARB1 modulators are being developed for:
- ALS: AAV-mediated ADARB1 gene delivery to motor neurons
- AD: Small molecule activators to restore editing
- Brain delivery: Enhancing CNS penetration of therapeutic agents
- Enzyme activators: Compounds enhancing ADARB1 catalytic activity
- RNA-based therapeutics: Oligonucleotides targeting specific editing sites
| Model |
Phenotype |
Key Findings |
| ADARB1 Knockout mice |
Embryonic lethal |
Essential for development |
| Conditional KO |
Motor neuron loss |
GluR2 editing critical |
| ADARB1ki mice |
Normal |
Editing-deficient GluR2 causes neurodegeneration |
- Biomarker potential: ADARB1 expression in blood may serve as a biomarker for neurodegeneration
- Therapeutic target: Restoring ADARB1 function is a promising approach
- Genetic variants: ADARB1 polymorphisms associated with neurological disease risk