| Raptor (Regulatory-Associated Protein of mTOR) |
|---|
| Gene | [RPTOR](/genes/rptor) |
| UniProt ID | [Q8N122](https://www.uniprot.org/uniprot/Q8N122) |
| PDB | 6BCX, 6U62, 7EHG |
| Molecular Weight | 149 kDa |
| Localization | Cytoplasm, lysosome surface |
| Family | WD40 repeat protein family |
| Disease | Cancer, AD, ALS, Autophagy disorders |
Raptor (Regulatory-associated protein of mTOR) is a critical scaffold protein that defines mTORC1 (mechanistic target of rapamycin complex 1). Raptor binds mTOR and recruits substrates for phosphorylation, including key regulators of protein synthesis, autophagy, and metabolism. mTORC1 signaling through Raptor coordinates cellular responses to nutrients, growth factors, and energy status, making it central to neurodegeneration through autophagy dysregulation.
Raptor has several functional domains:
- N-terminal RNC (Raptor N-terminal Conserved) domain: Conserved across species
- HEAT repeats: Mediate protein-protein interactions
- WD40 repeat domain (C-terminal): Forms β-propeller for substrate recognition
- TOS-binding site: Recognizes TOS (TOR signaling) motif on substrates
- Rag GTPase binding domain: Mediates lysosomal recruitment
Raptor interacts with:
- mTOR kinase: Core catalytic subunit
- mLST8/GβL: Stabilizes complex
- DEPTOR: Inhibitory subunit
- PRAS40: Inhibitory, released upon growth factor signaling
- Rag GTPases: Recruit mTORC1 to lysosome
mTORC1 (defined by Raptor) controls:
- Protein Synthesis: Phosphorylates S6K1 and 4E-BP1 → Translation initiation
- Autophagy: Phosphorylates ULK1/ATG13 → Inhibits autophagy initiation
- Lipid Synthesis: Activates SREBP transcription factors
- Mitochondrial Biogenesis: Inhibits PGC-1α, controls TFAM
- Lysosomal Function: TFEB phosphorylation (cytoplasmic retention)
- Cell Growth: Coordinates anabolic programs
mTORC1 activation pathway:
- Growth factors → PI3K/AKT → TSC2 inhibition → Rheb-GTP → mTORC1
- Amino acids → Rag GTPases → Lysosomal recruitment
- Energy → AMPK → TSC2 activation (inhibition)
mTORC1 hyperactivity in AD contributes to pathology:
Autophagy inhibition:
- Hyperactive mTORC1 blocks autophagy initiation
- Impaired Aβ and tau clearance
- Protein aggregate accumulation
- Rapamycin (mTORC1 inhibitor) reduces AD pathology in models
Tau interaction:
- mTORC1 hyperactivity promotes tau synthesis
- Rapamycin reduces tau levels
- mTORC1 inhibition enhances tau autophagic clearance
Aβ effects:
- Aβ oligomers may activate mTORC1
- Creating a feed-forward loop
- Impaired Aβ clearance
Synaptic effects:
- mTORC1 regulates protein synthesis at synapses
- Hyperactivity may disrupt synaptic plasticity
- Impaired memory consolidation
mTORC1 in PD:
- α-synuclein accumulation: Autophagy inhibition contributes
- Mitophagy: mTORC1 inhibits PINK1/Parkin pathway indirectly
- Dopaminergic neuron death: Rapamycin neuroprotective in models
¶ ALS and FTD
mTORC1 dysregulation in motor neuron disease:
- TDP-43: mTORC1 affects TDP-43 aggregation
- C9orf72: May interact with mTOR pathway
- Autophagy failure: Contributes to motor neuron degeneration
- Rapamycin: Mixed results in ALS models
- mHtt inhibits mTORC1 paradoxically
- Compensatory autophagy induction
- Complex role in HD pathophysiology
| Agent |
Mechanism |
Status |
| Rapamycin (Sirolimus) |
FKBP12-raptor allosteric inhibitor |
FDA approved (transplant) |
| Everolimus |
Rapamycin analog |
FDA approved (cancer) |
| Temsirolimus |
Rapamycin analog |
FDA approved (cancer) |
| Torin1/Torin2 |
ATP-competitive mTOR inhibitor |
Research tool |
| AZD8055 |
Dual mTORC1/mTORC2 inhibitor |
Phase I (cancer) |
| RapaLink-1 |
Bivalent mTOR inhibitor |
Preclinical |
Challenges with mTORC1 inhibition:
- Feedback activation of PI3K/AKT
- mTORC2 inhibition (long-term rapamycin)
- Immunosuppression
- Metabolic effects