| AGO2 Protein |
|---|
| Protein Name | Argonaute RISC Component 2 |
| Gene | [AGO2](/genes/ago2) |
| UniProt ID | [Q9UQ21](https://www.uniprot.org/uniprot/Q9UQ21) |
| PDB ID | 4w5n, 4w5r, 5oui |
| Molecular Weight | ~97 kDa |
| Subcellular Localization | Cytoplasm, P-bodies, Stress granules |
| Protein Family | Argonaute family, PIWI/AGO superfamily |
| Expression | Ubiquitous; high in brain, heart, muscle |
AGO2 (Argonaute RISC Component 2) is the central effector protein of the RNA-induced silencing complex (RISC), mediating microRNA (miRNA) and small interfering RNA (siRNA)-guided gene silencing. It is the only Argonaute with catalytic slicer activity in humans, enabling it to cleave target RNAs, making it essential for both miRNA-mediated repression and siRNA-mediated RNA interference.[1]
AGO2 contains multiple conserved domains that orchestrate small RNA binding and target cleavage:
¶ N-Terminal Domain
- Lobes N-terminal: Flexible region involved in small RNA loading
- Contains the slicer-independent silencing functions
¶ PAZ Domain (PIWI-Argonaute-Zwille)
- Binds the 3' end of small RNAs (miRNAs, siRNAs)
- Recognizes the 2-nucleotide 3' overhang of duplex siRNAs
- Anchors the guide strand while the passenger strand is discarded
¶ Mid Domain
- Binds the 5' phosphate of the guide small RNA
- Contains the seed region (nucleotides 2-8) that mediates target recognition
- Interfaces with GW182 for miRNA-mediated silencing
¶ PIWI Domain
- Contains the catalytic DEDH Asp triad (D597, D669, D709)
- Possesses endonucleolytic slicer activity
- Binds the guide-target RNA duplex central region
- Connect domains for conformational flexibility
- Allosteric regulation of catalytic activity
AGO2 is the core component of miRNA-induced silencing:[2]
- Pre-miRNA processed by Dicer to ~22 nt miRNA duplex
- miRNA duplex loaded onto AGO2
- Passenger strand ejected; mature miRNA-AGO2 complex formed
- miRNA "seed region" (nucleotides 2-8) pairs with complementary sites in target mRNA 3' UTRs
- Additional pairing downstream supports stable binding
- Multiple miRNA binding sites cooperatively enhance repression
- Transcriptional: Rarely, miRNA-AGO2 complexes enter nucleus to modulate transcription
- Post-transcriptional:
- Translation inhibition (initiation and elongation blocks)
- mRNA destabilization (deadenylation and decay)
- Ribosome drop-off
AGO2's catalytic activity enables:
- siRNA-mediated cleavage: Complete complementarity leads to target mRNA cleavage
- miRNA "slicing": In rare cases of near-perfect complementarity
- miRNA maturation: Some pri-miRNA processing by nuclear AGO2
AGO2 also mediates:
- miRNA-independent gene regulation
- Cellular stress responses
- Telomere maintenance
AGO2 dysfunction contributes to AD pathogenesis through multiple mechanisms:[3]
- Altered miRNA processing: Global miRNA dysregulation in AD brains
- Amyloid processing: AGO2 regulates APP and BACE1 expression via miRNAs
- Tau pathology: miRNA-AGO2 targeting of tau kinases and phosphatases
- Synaptic dysfunction: miRNA-AGO2 dysregulation affects synaptic proteins
- Neuronal vulnerability: Reduced AGO2 activity in AD neurons
- Alpha-synuclein aggregation affects miRNA processing[4]
- AGO2 involved in regulating LRRK2 expression
- miRNA dysregulation in PD substantia nigra
- AGO2 mutations cause familial ALS[5]
- Altered miRNA processing in motor neurons
- Stress granule dynamics affected
- Mutant HTT sequesters AGO2
- Global miRNA dysregulation
- Derepression of beneficial miRNA targets
AGO2 is frequently overexpressed in cancers:
- Promotes tumor growth and metastasis
- Therapeutic target under investigation
- Regulates oncogenes and tumor suppressors via miRNAs
- Essential for neuronal development
- Regulates neurogenesis
- Controls axon guidance
- Modulates synaptic plasticity
- miRNA mimics: Restore beneficial miRNA levels
- miRNA antagonists (antagomirs): Block pathogenic miRNAs
- AGO2 modulators: Enhance or inhibit function
- AGO2 enables siRNA-based gene silencing
- Being developed for neurodegenerative targets
- Delivery to brain remains challenge
- AGO2 inhibitors: Being developed to block oncogenic miRNA function
- Combination with chemotherapy: Sensitize tumors
- siRNA delivery: Exploit AGO2's slicer activity
- Meister et al., Mol Cell (2004): Identification of AGO2 as slicer
- Yuan et al., Nat Struct Mol Biol (2005): Crystal structure of AGO2 PAZ domain
- Nelson et al., Nat Rev Neurol (2017): miRNA dysregulation in AD
- Wakimoto et al., J Neurosci (2019): AGO2 in PD and alpha-synuclein
- Rybak-Wolf et al., Nat Rev Neurosci (2015): Non-canonical functions of AGO2
[1] Argonaute proteins: Evolution and function (2020)
[2] Mechanisms of miRNA-mediated silencing (2013)
[3] MicroRNA in Alzheimer's disease (2017)
[4] AGO2 and alpha-synuclein in PD (2019)
[5] AGO2 mutations in ALS (2018)
[6] Therapeutic potential of RNA interference (2021)