The 260-kDa transforming growth factor (TGF)-beta binding protein in rat glomeruli is a complex comprised of 170- and 85-kDa TGF-beta binding proteins.

In a previous study (MacKay, K., Robbins, A. R., Bruce, M. D., and Danielpour, D. (1990) J. Biol. Chem. 265, 9351-9356) we showed that rat glomeruli contain transforming growth factor (TGF)-beta 1 binding proteins with apparent molecular masses of 260, 170, and 85 kDa (Gl-260, Gl-170, Gl-85) as determined by electrophoresis under nonreducing conditions. We demonstrate here that Gl-260 is a complex of 170- and 85-kDa TGF-beta binding proteins. Under denaturing conditions the integrity of Gl-260 is maintained through the cross-linking of one monomer of the disulfide-linked TGF-beta 1 homodimer to Gl-85 and of the other monomer to the 100-kDa subunit of Gl-170. In addition, some Gl-260 complexes are maintained by direct cross-linking of Gl-85 to the 100-kDa subunit of Gl-170. One-dimensional peptide maps of Gl-85 and the 100-kDa subunit of Gl-170 indicate that they have distinctly different ligand binding domains. In contrast, peptide maps of Gl-85 and the type II receptor of normal rat kidney fibroblasts are similar. The biological responses of isolated glomeruli to TGF-beta appear to parallel those of cultured glomerular cells which are without detectable Gl-170 and Gl-260 binding proteins.