TGF-BETA-1 BINDING-PROTEIN - A COMPONENT OF THE LARGE LATENT COMPLEX OF TGF-BETA-1 WITH MULTIPLE REPEAT SEQUENCES

TGF-β occurs in a latent complex of high Mr. We report the cDNA cloning and an initial structural and functional characterization of a component of the large latent TGF-β1 complex, denoted TGF-β1 binding protein (TGF-β1-BP). Most of the sequence of fibroblast TGF-β1-BP is made up of cysteine-rich repeats of two different kinds; there are 16 EGF-like repeats and three repeats with a distant resemblance to EGF, but of a distinct type hitherto not found in any other protein. β-hydroxylated asparagine residues were identified in two of the EGF-like repeats. TGF-β1-BP purified from human platelets is considerably smaller than the fibroblast form (125-160 kd vs. 170-190 kd), suggesting that there is alternative splicing of the TGF-β1-BP gene or that TGF-β1-BP undergoes cell-specific proteolysis. TGF-β1-BP was found not to bind and inactivate TGF-β1; its role in the latent complex is discussed. © 1990.