Mapping the heparin-binding site on the 13-14F3 fragment of fibronectin

Abstract

Fibronectin, a multifunctional glycoprotein of the extracellular matrix, plays a major role in cell adhesion. Various studies have revealed that the human 13th and 14th fibronectin type III domains (labeled 13F3 and 14F3 here) contain a heparin-binding site. Mapping of the heparin-binding sites of 13-14F3, 13F3, and 14F3 by NMR chemical shift perturbation, isothermal titration calorimetry, and molecular modeling show that 13F3 provides the dominant heparin-binding site and that the residues involved are within the first 29 amino acids of 13F3. Predictions from earlier biochemical and modeling studies as well as the x-ray structure of 12-14F3 were tested. It was shown that the positively charged residues that project into the solvent from the ABE face of the triple-stranded β sheet on 13F3 are involved in binding, but 14F3 does not appear to contribute significantly to heparin binding.