A SINGLE HEPARIN-BINDING REGION WITHIN THE FIBRINOGEN-LIKE DOMAIN IS FUNCTIONAL IN CHICK TENASCIN-C

Tenascin-C binds to cell surface and matrix proteoglycans and to hepar in. Two heparin binding regions have recently been localized per tenas cin-C monomer, one in the C-terminal fibrinogen-like domain and the ot her in fibronectin type III repeats 3-5. Here we show that a single re gion in each subunit is necessary and sufficient for heparin binding b y whole tenascin-C at physiological ionic strength. First, native tena scin-C was bound to heparin-agarose and digested with Pronase. A 29-kD a fragment retained on the heparin column was recognized by a monoclon al antibody against the fibrinogen-like domain. In contrast, small fra gments labeled by an antibody against fibronectin type III repeats 2-5 were released. Second, mild tryptic digestion of tenascin-C yielded t wo related fragments of 180 and 170 kDa. The latter missed part of the fibrinogen domain and had lost affinity for heparin, in contrast to t he former. Finally, chick tenascin-C constructs were recombinantly exp ressed in human cells. Whereas the complete protein and a mutant lacki ng fibronectin type III repeats 1-5 bound to heparin-agarose, recombin ant tenascin-C missing the C-terminal fibrinogen-like globe did not. T hus, whole chick tenascin-C contains one essential heparin binding reg ion per subunit, located in the fibrinogen-like domain within 10 kDa f rom the C terminus.