Fig. 2.

Schematic representation of the 2 different classes of neurotrophin receptors (p75^NTR, TRK: TrkA, TrkB, TrkC). The p75^NTR is a glycoprotein containing 4 cysteine-rich domains in its extracellular portion but no intracytoplasmic tyrosine kinase (TK) domain. However, p75^NTR is capable of signaling independent of TRK presence, amplifying the TRK signal when TRK is present (Chao and Bothwell, 2002). TRK receptors contain a signal peptide sequence, cystein clusters, and leucine-rich and Ig-like regions in their extracellular domains and possess an intracytoplasmic TK domain. Percentages of similarity between the 3 main TRK receptors (TrkA, TrkB, TrkC) for their extracellular region/TK domain are respectively indicated.