Figure 1.

Domain organization of the Trk neurotrophin receptors. This figure highlights the key structural elements of the Trk neurotrophin receptors; the extracellular ligand-binding domain comprising leucine-rich motifs (LRR1-3), two cysteine clusters (C1 and C2) and two immunoglobulin-like domains (Ig1 and Ig2), the transmembrane domain, and the intracellular tyrosine kinase domain. Critical tyrosine residues of the human TrkA intracellular domain are highlighted. Tyrosine residues at positions 670, 674, and 675 are located in the activation loop of the human TrkA tyrosine kinase domain. Tyrosine 490 forms a PTB binding motif (NPXpY) known to bind SHC and FRS2 (Obermeier et al., 1993b; Ong et al., 2000) and tyrosine 785 binds to PLCγ (Obermeier et al., 1993a). The juxtamembrane KFG motif is an ubiquitination site involved in receptor localization.