FIBRONECTIN SELF-ASSOCIATION IS MEDIATED BY COMPLEMENTARY SITES WITHIN THE AMINO-TERMINAL ONE-THIRD OF THE MOLECULE

The formation of a fibrillar fibronectin (FN) extracellular matrix req uires self-association of FN dimers. In this report, we show that the major sites for self-association are the amino-terminal repeats I-1-5 and the first type III repeats. Recombinant FNs and fragments were gen erated by baculovirus expression of cysteine-rich domains and by bacte rial expression of type III repeats as fusion proteins with maltose bi nding protein. When recombinant polypeptides were immobilized on micro titer wells, FN bound to 70-kDa amino-terminal fragment and to fusion proteins containing repeats III1-2 and III1-6 but not to other type II I repeats. Similar results were obtained with a gel overlay assay. fin ding was concentration-dependent and saturable. The amino-terminal bin ding site for III1-2 was further localized to repeats I-1-5. Therefore , at least two different sites for FN-FN interaction reside near the a mino terminus of the molecule. A model for the regulation of FN matrix assembly is proposed based on intramolecular interactions between the se amino terminal sites.