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 heparin. Two heparin binding regions have recently been localized per tenascin-C monomer, one in the C-terminal fibrinogen-like domain and the other in fibronectin type III repeats 3-5. Here we show that a single region in each subunit is necessary and sufficient for heparin binding by whole tenascin-C at physiological ionic strength. First, native tenascin-C was bound to heparin-agarose and digested with Pronase. A 29-kDa fragment retained on the heparin column was recognized by a monoclonal antibody against the fibrinogen-like domain. In contrast, small fragments labeled by an antibody against fibronectin type III repeats 2-5 were released. Second, mild tryptic digestion of tenascin-C yielded two related fragments of 180 and 170 kDa. The latter missed part of the fibrinogen domain and had lost affinity for heparin, in contrast to the former. Finally, chick tenascin-C constructs were recombinantly expressed in human cells. Whereas the complete protein and a mutant lacking fibronectin type III repeats 1-5 bound to heparin-agarose, recombinant tenascin-C missing the C-terminal fibrinogen-like globe did not. Thus, whole chick tenascin-C contains one essential heparin binding region per subunit, located in the fibrinogen-like domain within 10 kDa from the C terminus.