Complex formation of a brain-derived neurotrophic factor and glycosaminoglycans.

Glycosaminoglycans (GAGs), large anionic glycopolymers, are the glycan portion of proteoglycans and are important components of the extracellular matrix. Recently we reported that polysialic acid, a polyanionic glycopolymer specific to the brain, binds neurotrophic factors to form a large complex. It is not clear whether GAGs also bind neurotrophic factors to form a large complex. In the present study, we demonstrate that a brain-derived neurotrophic factor (BDNF) dimer directly binds GAGs other than chondroitin and hyaluronic acid to form a large complex. Neurotrophin-3 showed similar GAG binding properties. Furthermore, BDNF, after forming a large complex with GAG, bound to the BDNF receptors tropomyosin-related kinase (Trk) B and p75 neurotrophin receptor (NTR). These findings suggest that GAGs function to produce a reservoir of BDNF and other neurotrophic factors, and may serve to regulate their local concentrations on the cell surface.