Characterization of aggrecan retained and lost from the extracellular matrix of articular cartilage - Involvement of carboxyl-terminal processing in the catabolism of aggrecan

The catabolism of aggrecan in bovine articular cartilage explants is characterized by the release into the culture medium of high molecular weight aggrecan fragments, generated by the proteolytic cleavage of the core protein between residues Glu(373) and Ala(374) within the interglobular domain. In this study, the position of the carboxyl-terminus of these aggrecan fragments, as well as a major proteolytically shortened aggrecan core protein present in cartilage matrix, have been deduced by characterizing the peptides generated by the reaction of aggrecan core protein peptides with cyanogen bromide. It was shown that two out of three such peptide fragments having an amino terminus starting at Ala(374) have their carboxyl terminus located within the chondroitin sulfate 1 domain. The third and largest aggrecan core protein peptide, with an amino terminus starting at Ala(374), has a carboxyl terminus in a region of core protein between the chondroitin sulfate 1 domain and the chondroitin sulfate 2 domain. The carboxyl terminus of this peptide appeared to be the same as that of the proteolytically degraded aggrecan core protein, which is retained within the extracellular matrix of the tissue. Another two aggrecan fragments recovered from the medium of explant cultures with amino-terminal sequences in the chondroitin sulfate 2 domain at Ala(1772) and Leu(1872) were shown to have their carboxyl termini within the G3 globular domain. These results suggest that the catabolism of aggrecan between residues Glu(373) and Ala(374) in the interglobular domain by the putative proteinase, aggrecanase, may be dependent on prior proteolytic processing within the carboxyl-terminal region of the core protein.