Binding of heparan sulfate to type V collagen. A mechanism of cell-substrate adhesion.

The functions and molecular interactions of type V collagen in the pericellular matrix are unclear. Our studies show that type V collagen adsorbed on a surface binds heparin/heparan sulfate with apparent higher affinity than do collagen types I, II, III, IV, or VI, fibronectin, or laminin. Therefore, heparin-like molecules may mediate interactions between cells and type V collagen. Hence, type V collagen may act as an anchor for proteoglycans in the extracellular matrix and function as a substrate for glycosaminoglycan-mediated cell attachment. This model is supported by studies showing that Chinese hamster ovary (CHO) cell mutants which are deficient in glycosaminoglycan synthesis attach poorly to type V collagen substrates compared to wild-type cells, whereas attachment of CHO cell mutants to fibronectin substrates is not affected. Also, exogenous heparin reduces attachment of CHO, endothelial, and smooth muscle cells to type V collagen but does not affect cell attachment to fibronectin. The inhibitory activity of the exogenous heparin/heparan sulfate depends on the size and sulfate content of the polysaccharide chains. At tested concentrations, chondroitin sulfate does not affect the attachment of CHO cells or the binding of biotin-conjugated heparan sulfate to wells coated with type V collagen. These data suggest that a certain degree of structural specificity is involved in glycosaminoglycan binding to type V collagen.