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O‐Linked Oligosaccharide on the 75‐kDa Neurotrophin Receptor

Abstract: Four neurotrophic factors, important for survival and function of neurons, bind a common receptor, the 75‐kDa neurotrophin receptor (NTR). An O‐glycosylated peptide connects the ligand‐binding domain of NTR to its transmembrane helix. This peptide, the transmembrane helix, and intracellular 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. Addition during biosynthesis of O‐linked glycans was evaluated, and structures were characterized by lectin blotting and glycosidase digestion. 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 structure assessed by mobility in polyacrylamide gels. NTR O‐linked glycans synthesized by cultured cells had the structure (NeuNAc)1–2‐Galβ1‐3GalNAc. 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 potential role for the stalk region in ligand binding and signaling.