DECORIN CORE PROTEIN-FRAGMENT LEU155-VAL260 INTERACTS WITH TGF-BETA BUT DOES NOT COMPETE FOR DECORIN BINDING TO TYPE-I COLLAGEN

It has been shown that small proteoglycans containing leucine-rich rep eats in their core proteins can form complexes with TGF-beta. Decorin, a ubiquitously found molecule of the extracellular matrix, is the bes t-studied example. Therefore, binding domains on its core protein were investigated using recombinant decorin fragments generated as fusion proteins in prokaryotes. The peptide Leu155-Val260 immobilized by the polyhistidine tag on a nickel chelate column bound TGF-beta 1 and -bet a 2 almost as effectively as the largest fragment (Asp45-Lys359) studi ed. Other peptides were less effective. For the two peptides Asp45-Lys 359 and Leu155-Val260 dissociation constants in the nanomolar range fo r high-affinity binding sites were calculated in a solid-phase assay w ith immobilized TGF-beta 2. Peptide Asp45-Lys359 also contained a lowe r affinity binding site. Domains with lower affinity were also found i n peptides Asp45-Leu155 and Arg63-Gly190. Peptide Leu155-Val260 also f ormed complexes with TGF-beta in the liquid phase as determined by equ ilibrium gel filtration. Furthermore, F(ab') fragments of polyclonal a ntibodies against peptide Leu155-Val260 interfered with TGF-beta bindi ng to peptide Asp45-Lys359 in a dose-dependent manner. Peptide Leu155- Val260, however, is only a weak competitor of the binding of wild-type decorin to reconstituted type I collagen fibrils. Therefore, independ ent binding sites of decorin for TGF-beta and type I collagen should e xist. In support of this hypothesis saturable binding of TGF-beta 1 an d TGF-beta 2 to collagen-bound native decorin could be demonstrated. T he bound cytokine could be released in a biologically active form by c ollagenase treatment. Thus, decorin may play a biological role in stor ing this cytokine temporarily in the extracellular matrix and in there by modulating an interaction of TGF-beta with its signaling receptors. (C) 1998 Academic Press.