The p75 neurotrophin receptor (p75^NTR) is a member of the tumor necrosis factor (TNF) receptor superfamily. Like all members of this superfamily, p75^NTR is a type I transmembrane protein with tandem cysteine-rich domains in its extracellular portion, as well as an intracellular death domain. p75^NTR binds to its ligands as a homodimer but can also form heterodimers with other receptors such as TrkA, TrkB, TrkC, Nogo receptor, and sortilin. The precise multimeric receptor complex formed between p75^NTR and the other receptors determine the ligand being recognized (see below) and the biological response to its binding^1-3.

As its name implies, p75^NTR binds to all the neurotrophins (NTR) (NGF, BDNF, NT-3, and NT-4) with similar nanomolar affinities. Co-expression of p75^NTR with the Trk receptors enhances its ability to bind and respond to the specific neurotrophin and induces cell survival. On the other hand, it has recently been demonstrated that p75^NTR binds with high affinity to the unprocessed form of NGF (proNGF), probably as a complex with sortilin, leading to cell death by apoptosis^1-3. Finally, a multimeric complex of p75^NTR and Nogo receptor binds to myelin proteins such as Nogo-66, MAG, and OmgP, resulting in inhibition of axonal growth⁴.