Characterization of type XI collagen-glycosaminoglycan interactions

Using competitive binding experiments, it was found that native type XI col lagen binds heparin, heparan sulfate, and dermatan sulfate. However, intera ctions were not evident with hyaluronic acid, keratan sulfate, or chondroit in 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 s ignificantly reduced attachment to type XI collagen, Incubation of denature d and cyanogen bromide-cleaved type XI collagen with radiolabeled heparin i dentified sites of interaction on the alpha1(XI) and alpha2(XI) chains. NH2 -terminal sequence data confirmed that the predominant heparin-binding pept ide contained the sequence GKPGPRGQRGPTGPRGSRGAR from the alpha1(XI) chain. Using rotary shadowing electron microscopy of native type XI collagen mole cules and heparin-bovine serum albumin conjugate, an additional binding sit e was identified at one end of the triple helical region of the collagen mo lecule. This coincides with consensus heparin binding motifs present at the aminoterminal ends of both the alpha1(XI) and the alpha2(XI) chains. The c ontribution of glycosaminoglycan-type XI collagen interactions to cartilage matrix stabilization is discussed.