Characterization of Type XI Collagen-Glycosaminoglycan Interactions

Using competitive binding experiments, it was found that native type XI collagen binds heparin, heparan sulfate, and dermatan sulfate. However, interactions were not evident with hyaluronic acid, keratan sulfate, or chondroitin sulfate chains over the concentration range studied. Chondrocyte-matrix interactions were investigated using cell attachment to solid phase type XI collagen. Pretreatment of chondrocytes with either heparin or heparinase significantly reduced attachment to type XI collagen. Incubation of denatured and cyanogen bromide-cleaved type XI collagen with radiolabeled heparin identified sites of interaction on the α1(XI) and α2(XI) chains. NH2-terminal sequence data confirmed that the predominant heparin-binding peptide contained the sequence GKPGPRGQRGPTGPRGSRGAR from the α1(XI) chain. Using rotary shadowing electron microscopy of native type XI collagen molecules and heparin-bovine serum albumin conjugate, an additional binding site was identified at one end of the triple helical region of the collagen molecule. This coincides with consensus heparin binding motifs present at the amino-terminal ends of both the α1(XI) and the α2(XI) chains. The contribution of glycosaminoglycan-type XI collagen interactions to cartilage matrix stabilization is discussed.