AN UNUSUAL HEPARIN-BINDING PEPTIDE FROM THE CARBOXY-TERMINAL HEP-2 REGION OF FIBRONECTIN

A synthetic 22 residue peptide, N22W, with sequence NVSPPRRARVTDATETTI TISW, derived from the amino terminus of type III module 13 in the car boxyterminal hep-2 domain of fibronectin, was found to exhibit unusual heparin binding properties. Titration of fluoresceinamine-labeled hep arin (FA-heparin) with N22W at 25 degrees C and pH 7.4 in 0.02 M Tris buffer containing 0.15 M NaCl (TBS) produced a cooperative sigmoidal i ncrease in fluorescence polarization anisotropy with half-saturation n ear 2.5 mu M. The increase in anisotropy was even greater than that pr oduced by the much larger 30-kDa hep-a fragment of fibronectin and sat uration was achieved at lower concentration. Simply deleting the C-ter minal Trp from the peptide abolished its heparin-binding activity as d id deletion of residues TETTITIS or mutation of the RR doublet to SS. Further analysis suggested that peptide-peptide interactions mediated by the carboxy-terminal region of N22W play an important role in its b inding to heparin. A branched tetrameric peptide containing four copie s of N21S caused a nearly hyperbolic increase in anisotropy of FA-hepa rin with an apparent K-d of 0.3 mu M in TBS, 10-fold lower than that o f the monomer or of the parent domain from which the peptide was deriv ed. The results illustrate that peptide-peptide interactions can lead to stronger binding by allowing multiple points of contact with the ne gatively charged polysaccharide. (C) 1994 Academic Press, Inc.