The Best Prion Protein Linking to Focal Adhesion Kinase (FAK): Cellular Prion Protein (PrPC)
Based on the available molecular and structural data, the cellular prion protein (PrPC) is the prion protein variant that functionally links to focal adhesion kinase (FAK). However, this linkage is indirect — it operates through a well-characterized signaling cascade mediated by intermediate proteins, all of which have known or partially solved molecular structures.
1. The Linkage Pathway: PrPC → Src-Family Kinases → FAK
PrPC is a glycosylphosphatidylinositol (GPI)-anchored protein that lacks a cytoplasmic domain, so it cannot directly bind or phosphorylate FAK. Instead, the connection occurs through an established signaling route:
| Step | Component | Molecular Structure Status |
|---|---|---|
| 1 | PrPC (cellular prion protein) | C-terminal globular domain solved by NMR/X-ray (e.g., PDB: 1QM0, 1HJM); N-terminal region is intrinsically disordered |
| 2 | Transmembrane receptors (e.g., 37/67 kDa laminin receptor LR/LRP/RPSA, NCAM) | LR structure partially solved; PrPC–LR binding interface mapped |
| 3 | Src-family kinases (especially Fyn) | SH2, SH3, and kinase domain structures solved (e.g., PDB: 2DQ7 for Fyn kinase) |
| 4 | Focal Adhesion Kinase (FAK) | FERM domain crystal structure solved (PMID: 16221668); kinase domain and FAT domain structures available |
How It Works
- PrPC binds to cell-surface transmembrane partners — most prominently the 37/67 kDa laminin receptor (RPSA), which has high binding affinity for PrPC.
- This binding triggers clustering in lipid raft microdomains and activates Src-family kinases (primarily Fyn).
- Activated Fyn then phosphorylates FAK at Tyr-397 (the FAK autophosphorylation site), leading to FAK activation.
- The active FAK–Src complex drives downstream signaling affecting focal adhesion dynamics, cell spreading, and migration.
2. Key Evidence for the PrPC–FAK Link
| Finding | Source |
|---|---|
| PrPC modulates focal adhesion formation and filopodia extension | PubMed ID 19116153 |
| PrPC accumulates in focal adhesions when overexpressed | PubMed ID 19116153 |
| PrPC signaling activates FAK, HSP27, and p38 phosphorylation | Taylor & Hooper, 2012 |
| PrPC activates Src-family kinases (SFKs) including Fyn | Multiple studies |
| FAK–Src kinase complex is a central mediator of integrin signaling | PMC25619, various |
3. Why the 37/67 kDa Laminin Receptor Is the Best Structural Linker
The 37/67 kDa laminin receptor (LR/LRP/RPSA) is particularly important because:
- It is the best-characterized cell-surface receptor for PrPC with known binding domains.
- It directly connects to integrin signaling and focal adhesion pathways.
- Its structure (37 kDa precursor form) has been characterized.
- The PrPC–LR interaction has been mapped to specific regions: PrPC binds LR via its N-terminal region (residues 144–179) and the octapeptide repeat region.
- LR then signals through integrins and Src-family kinases to activate FAK.
4. Existing Structural Models for Key Interactions
| Interaction | Structural Information |
|---|---|
| PrPC C-terminal domain | Solved (e.g., PDB: 1QM0 — human PrPC globular domain) |
| FAK FERM domain | Crystal structure solved (avian; PMID: 16221668) |
| FAK kinase domain | Crystal structures available (e.g., PDB: 2J0L, 2J0K) |
| Fyn SH2/SH3/kinase domains | Multiple crystal structures available |
| 37 kDa laminin receptor | Structural model available; binding interface with PrPC mapped |
| PrPC–NCAM FN domain interaction | Molecular details reported (JBC, 2012) |
5. Summary: Best Candidate
The cellular prion protein (PrPC) is the prion protein that links to FAK, but this linkage is indirect and mediated by well-characterized signaling intermediates:
PrPC → 37/67 kDa Laminin Receptor (or NCAM/other receptors) → Src-family Kinases (Fyn) → FAK (Tyr397 phosphorylation)
No direct PrPC–FAK protein–protein interaction has been structurally demonstrated. Rather, the connection is indirect and mediated by well-characterized signaling intermediates, all of which have known or partially solved molecular structures. If you need a single “linker” protein with known structure between PrPC and FAK, the 37/67 kDa laminin receptor is the best candidate that physically binds PrPC and lies upstream of the Src→FAK signaling axis.
