Recombinant soluble betaglycan is a potent and isoform-selective transforming growth factor-beta neutralizing agent

Betaglycan is an accessory receptor of members of the transforming growth f actor-beta (TGF-beta) superfamily, which regulates their actions through li gand-dependent interactions with type TI receptors. A natural soluble Form of betaglycan is found in serum and extracellular matrices. Soluble betagly can, prepared as a recombinant protein using the baculoviral expression sys tem, inhibits the actions of TGF-beta. Because of its potential use as an a nti-TGF-beta therapeutic agent, we have purified and characterized baculovi ral recombinant soluble betaglycan. Baculoviral soluble betaglycan is a hom odimer formed by two 110 kDa monomers associated by non-covalent interactio ns. This protein is devoid of glycosaminoglycan chains, although it contain s the serine residues, which, in vertebrate cells, are modified by these ca rbohydrates. On the other hand, mannose-rich carbohydrates account for appr oximately 20 kDa of the mass of the monomer. End-terminal sequence analysis of the soluble betaglycan showed that Gly(24) is the first residue of the mature protein. Similarly to the natural soluble betaglycan, baculoviral so luble betaglycan has an equilibrium dissociation constant (K-d) of 3.5 nM f or TGF-beta1. Ligand competition assays indicate that the relative affiniti es of recombinant soluble betaglycan for the TGF-beta isoforms are TGF-beta (2)>TGF-beta (3)>TGF-beta1. The anti-TGF-beta potency of recombinant solub le betaglycan in vitro is 10-fold higher for TGF-beta2 than for TGF-beta1. Compared with a commercial pan-specific anti-TGF-beta neutralizing antibody , recombinant soluble betaglycan is more potent against TGF-PZ and similar against TGF-beta1. These results indicate that baculoviral soluble betaglyc an has the biochemical and functional properties that would make it a suita ble agent for the treatment of the diseases in which excess TGF-beta plays a central physiopathological role.