NGF BINDING TO THE TRK TYROSINE KINASE RECEPTOR REQUIRES THE EXTRACELLULAR IMMUNOGLOBULIN-LIKE DOMAINS

Neurotrophins initiate their biological effects by activating members of the trk tyrosine kinase subfamily. The extracellular region of trk receptors is distinguished by several common structural features, incl uding leucine-rich repeats, clusters of cysteine-rich domains, and two immunoglobulin-like domains. However, the receptor sequences required for ligand binding have not been localized. In order to define the do mains involved in NGF binding, a series of chimeric receptors was cons tructed using cDNA sequences from rat trkA and trkB. The chimeric cons tructs were expressed after transient transfection in 293 cells and th e expression of each receptor was verified by immunoprecipitation and immunoblot analysis. Equilibrium binding of transfected cells revealed that the two IgG domains of trkA are essential for NGF binding. The r equirement for the two IgG domains was further confirmed by Scatchard analysis and affinity crosslinking with I-125-NGF. These results indic ate that NGF binding is crucially dependent upon interactions with the IgG domains Of the trkA receptor. (C) 1995 Academic Press, Inc.