Abstract

The interactions of the dermatan sulfate proteoglycans biglycan and decorin have been investigated with the elastic fiber components, tropoelastin, fibrillin-containing microfibrils, and microfibril-associated glycoproteins (MAGP) 1 and 2. Both proteoglycans were found to bind tropoelastin and fibrillin-containing microfibrils but not MAGPs 1 and 2 in solid phase binding assays. The specificity of the binding of biglycan and decorin to tropoelastin was confirmed by co-immunoprecipitation experiments and by the blocking of the interactions with elastin-derived peptides. Isolated core proteins from biglycan and decorin bound to tropoelastin more strongly than the intact proteoglycans, and there were no differences in the tropoelastin binding characteristics of distinct glucuronate-rich and iduronate-rich glycoforms of biglycan. These findings indicated that the binding sites were contained in the protein cores of the proteoglycans rather than the glycosaminoglycan side chains. Scatchard analysis showed that biglycan bound more avidly than decorin to tropoelastin with K(d) values estimated as 1.95 x 10(-7) m and 5.3 x 10(-7) m, respectively. In blocking experiments each proteoglycan showed extensive inhibition of binding of the other to tropoelastin but was most effective at blocking its own binding. This result suggested that biglycan and decorin had closely spaced but distinct binding sites on tropoelastin. Addition of the elastin-binding protein MAGP-1 to the assays enhanced the binding of biglycan to tropoelastin but had no effect on the decorin-tropoelastin interaction. Co-immunoprecipitation experiments showed that MAGP-1 interacted with biglycan but not decorin in the solution phase. The results indicated that biglycan specifically formed a ternary complex with tropoelastin and MAGP-1. Overall the study supports the concept that biglycan may have a specific role in the elastinogenic phase of elastic fiber formation.

Highlights

  • The small dermatan sulfate proteoglycans biglycan and decorin are constituents of extracellular matrices in a wide range of tissues [1, 2]

  • The results show that both proteoglycans interact with tropoelastin and microfibrils and that biglycan forms a ternary complex with tropoelastin and MAGP1

  • The microfibril-associated glycoproteins (MAGP)-1 pretreatment had no effect on the binding of decorin to tropoelastin. These findings suggested that MAGP-1 was not blocking the binding sites for decorin and biglycan on tropoelastin, and MAGP-1 appeared to have a binding site on the tropoelastin that was distinct from the biglycan- and decorin-binding sites

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Summary

Molecular Interactions of Biglycan and Decorin with Elastic Fiber Components

BIGLYCAN FORMS A TERNARY COMPLEX WITH TROPOELASTIN AND MICROFIBRIL-ASSOCIATED GLYCOPROTEIN 1*. The interactions of the dermatan sulfate proteoglycans biglycan and decorin have been investigated with the elastic fiber components, tropoelastin, fibrillin-containing microfibrils, and microfibril-associated glycoproteins (MAGP) 1 and 2. Both proteoglycans were found to bind tropoelastin and fibrillin-containing microfibrils but not MAGPs 1 and 2 in solid phase binding assays. In the present study we have investigated the interaction of decorin and biglycan glycoforms with the elastin precursor tropoelastin, MAGPs, and isolated fibrillin-containing, elastinassociated microfibrils. The results show that both proteoglycans interact with tropoelastin and microfibrils and that biglycan forms a ternary complex with tropoelastin and MAGP1 This is consistent with a specific role for biglycan in elastic fiber biology

EXPERIMENTAL PROCEDURES
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DISCUSSION

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