The effect of link protein on proteoglycan aggregate structure. An electron microscopic study of the molecular architecture and dimensions of proteoglycan aggregates reassembled from the proteoglycan monomers and link proteins of bovine fetal epiphyseal cartilage.

Proteoglycan monomer and link protein were prepared from bovine fetal epiphyseal cartilage. Proteoglycan aggregates were reassembled from proteoglycan monomers and hyaluronic acid in the presence or in the absence of link protein at pH 7 and at pH 5. The proteoglycan solutions were spread on nitrocellulose films and examined by electron microscopy. At pH 7, the aggregates formed in the presence of link protein showed dramatic differences in their dimensions, compared with the link protein-free aggregates. The link protein-containing aggregates were five times longer and contained three times as many monomers per aggregates. The mean distance between monomers was twice as long and the spacing between monomers was more regular in the link protein-containing aggregates. Essentially the same differences between link protein-free and link protein-containing proteoglycan aggregates were observed at pH 5. These results show that link protein increases proteoglycan aggregate size by facilitating the binding of more monomers to hyaluronic acid and influences the spacing of monomers along hyaluronic acid chains.