Role for carbohydrate structures in TGF-beta 1 latency.

Transforming growth factor-beta (TGF-beta) (reviewed in refs 1-3) is a family of molecules that are made up as disulphide-bonded dimers of at least three different types of homologous polypeptides. The active molecules are cleaved from the C termini of precursors. TGF-beta 1, like other forms of TGF-beta, is synthesized and secreted in a latent high relative molecular mass form (L-TGF-beta 1) from which active TGF-beta 1 can be released by transient and probably unphysiological acidification. The latent complex from human platelets contains one dimeric TGF-beta 1 molecules, which is noncovalently associated with a disulphide-bonded complex of one dimeric remnant of the precursor and a single molecule of the so-called TGF-beta 1 binding protein (TGF-beta 1-BP). We report here that enzymatic removal in vitro of the carbohydrate structures in the remnant of the TGF-beta 1 precursor produces biologically active TGF-beta 1 from the latent complex, suggesting that carbohydrate structures are of importance in rendering TGF-beta 1 inactive in the complex in vivo.