The effect of proteoglycans on the formation of fibrils from collagen solutions.

The precipitation of collagen fibrils from solutions at 37°C and approximately physiological pH and ionic strength is retarded markedly in the presence of small amounts of proteoglycan monomer (PGS), proteoglycan aggregate (PGC), reduced and alkylated PGS, or cyanogen bromide-cleavage products of PGS. The polysaccharide-peptide fragments produced from PGS with papain, trypsin, cathepsin D, or the protein core obtained by the digestion of PGS with chondroitinase ABC are ineffective in this regard. In the presence of the materials which affected the rate of precipitation of the collagen fibrils, the specific absorbance, AA,,, of the collagen gels was directly related to specific retardation, R,,, when the ratio of proteoglycan to collagen was less than 25 Fg/mg, suggesting that the size and/or organization of the fibrils in the gels was dependent on the presence of proteoglycans. PGS binds to collagen if it is present in the solution before the collagen tibrils form and at a maximum of about 1 molecule of PGS for every 25-30 molecules of collagen. Although the protein core of PGS does not retard fibrillogenesis, it does bind to collagen and does so even in the presence of PGS. The data support the thesis that the organization of collagen fibrils in tissues may be related to amounts and kinds of proteoglycans in the tissues.