Alternative splicing of the first F3 domain from chicken collagen XIV affects cell adhesion and heparin binding

The N terminus of chicken collagen XIV is subject to alternative splicing. The longer isoform contains a fibronectin type III (F3) domain at its N ter minus, whereas the shorter isoform is lacking this domain. Alternative spli cing of the F3 domain is developmentally regulated. At early embryonic stag es, both isoforms are expressed, whereas after hatching only the longer iso form is expressed. When immobilized on plastic dishes, the recombinant F3 d omain promotes the adhesion of mesenchymal cells. Attachment to this domain is specifically inhibited by heparin but not by other glycosaminoglycans, Molecular modeling studies illustrate that the first F3 domain harbors a po sitively charged groove, which may accommodate the negatively charged hepar in chain. Site-directed mutagenesis of a single lysine residue within this groove abolishes the cell binding activity but does not affect the heparin binding activity. Cell binding and heparin binding are therefore two functi onally distinct properties shared by the N-terminal F3 domain. When full-le ngth collagen XIV polypeptides that either contain or lack the first F3 dom ain are tested on heparin-Sepharose, a pronounced difference in their relat ive affinity is observed. Thus, alternative splicing of the N-terminal F3 d omain influences the interaction of this FACIT (fibril-associated collagens with interrupted triple helices) collagen with cells and with glycosaminog lycans.