The Structure in Solution of Fibronectin Type III Domain 14 Reveals Its Synergistic Heparin Binding Site

Fibronectin is a large multidomain protein of the extracellular matrix that harbors two heparin binding sites, Hep-I and Hep-II, which support the heparin-dependent adhesion of melanoma and neuroblastoma cells [Barkalow, F. J. B., and Schwarzbauer, J. E. (1991) J. Biol. Chem. 266, 7812–7818; McCarthy, J. B., et al. (1988) Biochemistry 27, 1380–1388; Drake, S. L., et al. (1993) J. Biol. Chem. 268, 15859–15867]. The stronger heparin/HS binding site on fibronectin, Hep-II, spans fibronectin type III domains 12–14. Previous site-directed mutagenesis, nuclear magnetic resonance (NMR) chemical shift perturbation, and crystallographic structural studies all agree that the main heparin binding site is located on the surface of fibronectin type III domain 13 [Ingham, K. C., et al. (1993) Biochemistry 32, 12548–12553; Sharma, A., et al. (1999) EMBO J. 18, 1468–1479; Sachchidanand, L. O., et al. (2002) J. Biol. Chem. 277, 50629−50635]. However, the “synergy site” for heparin binding located on fibronectin type III d...