Unraveling the amino acid sequence crucial for heparin binding to collagen V

We have previously shown that a recombinant 18-kDa fragment of the collagen alpha 1(V) chain (Ile(824)-Pro(950)), referred to as HepV, binds to heparin and heparan sulfate (Delacoux, F., Fichard, A, Geourjon, C., Garrone, R., and Ruggiero, F, (1998) J, Biol, Chem. 273, 15069-15076), No consensus sequence was found in the alpha 1(V) primary sequence, but a cluster of 7 basic amino acids tin the Arg(900)-Arg(924) region) was postulated to contain the heparin-binding site, The contribution of individual basic amino acids within this sequence was examined by site-directed mutagenesis, Further evidence for the precise localization of the heparin-binding site was provided by experiments based on the fact that heparin can protect the alpha 1(V) chain heparin-binding site from trypsin digestion. The results parallel the alanine scanning mutagenesis data, i.e. heparin binding to the alpha 1(V) chain involved Arg(912), Arg(918), and Arg(921) and two additional neighboring basic residues, Lys(905) and Arg(909), Our data suggest that this extended sequence functions as a heparin-binding site in both collagens V and XI, indicating that these collagens use a novel sequence motif to interact with heparin.