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 repeats in their core proteins can form complexes with TGF-beta. Decorin, a ubiquitously found molecule of the extracellular matrix, is the best-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-beta1 and -beta2 almost as effectively as the largest fragment (Asp45-Lys359) studied. Other peptides were less effective. For the two peptides Asp45-Lys359 and Leu155-Val260 dissociation constants in the nanomolar range for high-affinity binding sites were calculated in a solid-phase assay with immobilized TGF-beta2. Peptide Asp45-Lys359 also contained a lower affinity binding site. Domains with lower affinity were also found in peptides Asp45-Leu155 and Arg63-Gly190. Peptide Leu155-Val260 also formed complexes with TGF-beta in the liquid phase as determined by equilibrium gel filtration. Furthermore, F(ab') fragments of polyclonal antibodies against peptide Leu155-Val260 interfered with TGF-beta binding 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, independent binding sites of decorin for TGF-beta and type I collagen should exist. In support of this hypothesis saturable binding of TGF-beta1 and TGF-beta2 to collagen-bound native decorin could be demonstrated. The bound cytokine could be released in a biologically active form by collagenase treatment. Thus, decorin may play a biological role in storing this cytokine temporarily in the extracellular matrix and in thereby modulating an interaction of TGF-beta with its signaling receptors.
Schönherr
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E
Institute of Physiological Chemistry and Pathobiochemistry, University of Münster, Waldeyerstrasse 15, Münster, D-48149, Germany. schonhe@uni-muenster.de
Broszat
M
M
Brandan
E
E
Bruckner
P
P
Kresse
H
H
D001665:Binding Sites; D001667:Binding, Competitive; D002850:Chromatography, Gel; D003094:Collagen / Q000378:metabolism*; D058575:Decorin; D016326:Extracellular Matrix Proteins; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism / Q000494:pharmacology; D007930:Leucine / Q000378:metabolism; D009000:Monocytes; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014633:Valine / Q000378:metabolism
C546878:DCN protein, human; D058575:Decorin; D016326:Extracellular Matrix Proteins; D007106:Immune Sera; D007140:Immunoglobulin Fab Fragments; D010446:Peptide Fragments; D011509:Proteoglycans; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D003094:Collagen; D007930:Leucine; D014633:Valine