O-LINKED OLIGOSACCHARIDE ON THE 75-KDA NEUROTROPHIN RECEPTOR

Four neurotrophic factors, important for survival and function of neur ons, bind a common receptor, the 75-kDa neurotrophin receptor (NTR). A n O-glycosylated peptide connects the ligand-binding domain of NTR to its transmembrane helix, This peptide, the transmembrane helix, and in tracellular sequences are highly conserved in vertebrate evolution. To investigate the structure and function of O-glycosylation on NTR, we produced the extracellular domains by expression in mammalian cells. A ddition during biosynthesis of O-linked glycans was evaluated, and str uctures were characterized by lectin blotting and glycosidase digestio n. Effects of desialylation, deglycosylation, and lectin attachment on the equilibrium binding constant were measured, Addition of O-linked glycans during biosynthesis was found to have a large effect on NTR st ructure assessed by mobility in polyacrylamide gels. NTR O-linked glyc ans synthesized by cultured cells had the structure (NeuNAc)(1-2)-Gal beta 1-3GalNAc. Modification of the O-linked oligosaccharide produced small, possibly significant effects on the binding constant of NTR for nerve growth factor. The results are discussed in reference to a pote ntial role for the stalk region in ligand binding and signaling.