Purification of the transforming growth factor-beta (TGF-beta) binding proteoglycan betaglycan

We report the purification of betaglycan, a low-abundance membrane proteoglycan with high affinity for transforming growth factor-beta (TGF-beta). Betaglycan solubilized from rat embryo membrane preparations was purified to near-homogeneity by sequential chromatography through DEAE-Trisacryl, wheat germ lectin-Sepharose, and TGF-beta 1-agarose. Purified betaglycan has properties similar to betaglycan affinity-labeled in intact cells: it binds TGF-beta 1 and TGF-beta 2 with KD approximately 0.2 nM, contains heparan sulfate and chondroitin sulfate glycosaminoglycan (GAG) chains and N-linked glycans attached to a 110-kDa core protein, and can spontaneously associate with phosphatidylcholine liposomes. The betaglycan core obtained by enzymatic removal of the GAG chains has high affinity for TGF-beta and associates with artificial liposomes, indicating that the core protein binds TGF-beta and anchors to membranes independently of the GAG chains present on the native protein or of any ancillary protein.