TrkA Receptor Deep Dive
Nerve Growth Factor Receptor
This lesson uses the TrkA–NGF complex 1WWW, chain X. 1WWC is an NT-3–TrkC structure, not an alternative TrkA entry, and must not be used with these chain IDs or steering residues. The machine-readable source of truth is data/targets.yml.
Biological Context
Tropomyosin receptor kinase A (TrkA, NTRK1) is the high-affinity receptor for Nerve Growth Factor (NGF). NGF binding to the extracellular domain triggers dimerization, transphosphorylation of intracellular kinase domains, and downstream survival and differentiation signaling in sensory and sympathetic neurons.
Why it matters: The NGF/TrkA axis is a heavily studied pain target. The anti-NGF antibody tanezumab reached phase III for osteoarthritis pain, but its global program was discontinued in 2021 after regulatory benefit–risk concerns, including joint safety. Blocking TrkA directly, instead of sequestering NGF, is an alternative research strategy. On the oncology side, TrkA fusions drive a subset of solid tumors and are targeted by kinase inhibitors such as larotrectinib and entrectinib. A de novo extracellular binder would be a distinct, experimentally unvalidated modality.
The Goal: Design a binder that engages the NGF-binding face of TrkA’s d5 (membrane-proximal Ig-like) domain, competing with NGF.
Interactive Structure
The viewer below shows the extracellular d5 domain of TrkA (chain X) in complex with NGF (chains V, W) — note that the biological assembly is a 2:2 TrkA-d5 / NGF dimer.
Non-interactive alternative: The target-specification table below describes the relevant chains and interface residues. You can also open the 1WWW structure record or download its PDB coordinates. Manipulating the 3D viewer is optional.
- Rotate: Left-click and drag
- Zoom: Scroll wheel
- Pan: Right-click (or Ctrl+Left-click) and drag
Design Mission
Design a protein that binds to the NGF-binding face of TrkA d5.
Target Specifications
| Feature | Detail |
|---|---|
| Target Name | TrkA d5 domain (extracellular, membrane-proximal Ig-like) |
| PDB ID | 1WWW (TrkA–NGF; do not substitute 1WWC, an NT-3–TrkC structure) |
| Target Chain | Chain X (TrkA-d5) |
| Binder to mimic | Chains V, W (NGF dimer) |
| PDB-derived interface contacts (≤5 Å) | H291, V294–H298, C300, P302–S304, F327, L333–P335, H343–C345, R347, N349, Q350, T352–N355, M379–P382 |
| Candidate steering set | X303,X343,X347,X350,X353 (F303, H343, R347, Q350, H353), sampling the ABED β-sheet-facing contact surface |
These are every TrkA-d5 residue within 5 Å of NGF in 1WWW. They describe the observed interface geometry, not measured energetic hotspots. The smaller course set is a steering hypothesis that spans dense contacts on a large, relatively flat surface.
Strategy Tips
- Download PDB
1WWW. - Clean the structure: Keep Chain X (TrkA-d5). Remove NGF (V, W) and any crystallographic partners.
- Define steering residues: Begin with
X303,X343,X347,X350,X353in RFdiffusion / BindCraft, then compare coverage and pose diversity with at least one smaller subset. - Beware of loop flexibility: The AB loop of d5 (residues 294–304) is somewhat flexible; designs that make contacts almost exclusively with this loop may not survive in solution. Balance contacts between the rigid β-sheet core and the loops.
Reference
- Wiesmann, C., Ultsch, M.H., Bass, S.H., de Vos, A.M. (1999). Crystal structure of nerve growth factor in complex with the ligand-binding domain of the TrkA receptor. Nature 401, 184–188. doi:10.1038/43705 — primary citation for 1WWW.