HIGH-RESOLUTION MAPPING OF THE BINDING-SITE OF TRKA FOR NERVE GROWTH-FACTOR AND TRKC FOR NEUROTROPHIN-3 ON THE 2ND IMMUNOGLOBULIN-LIKE DOMAIN OF THE TRK RECEPTORS

Neurotrophic factors are important for survival and maintenance of neu rons during developmental and adult stages of the vertebrate nervous s ystem. The neurotrophins mediate their signal into the cell by specifi c interaction with tyrosine kinase receptors of the Trk family, The ex tracellular immunoglobulin-like domain of the Trk receptors adjacent t o the membrane has previously been shown to be the dominant element fo r specific neurotrophin binding. Using computer graphics models of the human TrkA and TrkC immunoglobulinlike domains as a guide, the residu es involved in binding to their respective neurotrophins were mapped b y mutational analysis. TrkC primarily utilizes loop EF, between beta-s trands E and F, for binding. In contrast, TrkA utilizes the EF loop as well as additional residues, the latter being prime candidates for de termining the specificity of TrkA versus TrkC, When selected TrkC and TrkA mutants with reduced binding were expressed on NIH3T3 cells, neur otrophin-induced autophosphorylation was strongly reduced or absent.