Unraveling the amino acid sequence crucial for heparin binding to collagenV

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 hepari n and heparan sulfate (Delacoux, F., Fichard, A, Geourjon, C., Garrone, R., and Ruggiero, F, (1998) J, Biol, Chem. 273, 15069-15076), No consensus seq uence was found in the alpha 1(V) primary sequence, but a cluster of 7 basi c amino acids tin the Arg(900)-Arg(924) region) was postulated to contain t he heparin-binding site, The contribution of individual basic amino acids w ithin this sequence was examined by site-directed mutagenesis, Further evid ence 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) ch ain heparin-binding site from trypsin digestion. The results parallel the a lanine scanning mutagenesis data, i.e. heparin binding to the alpha 1(V) ch ain involved Arg(912), Arg(918), and Arg(921) and two additional neighborin g basic residues, Lys(905) and Arg(909), Our data suggest that this extende d 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.