MOLECULAR-FEATURES OF THE COLLAGEN-V HEPARIN-BINDING SITE

A heparin binding region is known to be present within the triple heli cal part of the alpha 1(V) chain. Here we show that a recombinant alph a 1(V) fragment (Ile(284) to Pro(950)), referred to as HepV, is suffic ient for heparin binding at physiological ionic strength. Both native individual alpha 1(V) chains and HepV are eluted at identical NaCl con centrations (0.35 M) from a heparin-Sepharose column, and this binding can be inhibited specifically by the addition of free heparin or hepa ran sulfate. In contrast, a shorter as-residue synthetic peptide, cont aining the putative heparin binding site in HepV, fails to bind hepari n, Interestingly, HepV promotes cell attachment, and HepV-mediated adh esion is inhibited specifically by heparin or heparan sulfate, indicat ing that this region might behave as an adhesive binding site. The sam e site is equally functional on triple helical molecules as shown by h eparin-gold labeling. However, the affinities for heparin of each of t he collagen V molecular forms tested are different and increase with t he number of alpha 1(V) chains incorporated in the molecules. Molecula r modeling of a sequence encompassing the putative HepV binding sequen ce region shows that all of the basic residues cluster on one side of the helical face. A highly positively charged ring around the molecule is thus particularly evident for the alpha 1(V) homotrimer, This coul d strengthen its interaction with the anionic heparin molecules. We pr opose that a single heparin binding site is involved in heparin-relate d glycosaiminoglycans-collagen V interactions, but the different affin ities observed likely modulate cell and matrix interactions between co llagen V and heparan sulfate proteoglycans in tissues.