title: Link protein as a monitor in situ of endogenous proteolysis in adult human articular cartilage.
abstract: The link protein components of proteoglycan aggregates in adult human articular cartilage show heterogeneity due to proteolysis. Cleavages near the N-terminus of the intact link proteins, before residues 17, 19 and 24, generate three proteins of slightly diminished size (LP3). Cleavages within the N-terminal disulphide-bonded loop, before residues 66 and 73 of the intact link proteins, generate proteins that yield smaller degradation products upon reduction (LP fragments). In vitro, modified link protein components of a similar size to LP3 can be generated by a variety of proteinases, but of the physiologically relevant enzymes only stromelysin, cathepsin B and cathepsin G have the ability to yield modified link proteins with N-termini identical with those observed in situ. None of the proteolytic agents tested was able to produce LP fragments with N-termini identical with those observed in situ, and the majority of proteinases were not able to cleave within the disulphide-bonded loops. Cathepsin L and hydroxyl radicals can cleave within the N-terminal disulphide-bonded loop, and have the potential of initially opening the loop to allow further proteolytic processing by other agents to generate the native cleavage sites.
authors.affiliation: Joint Diseases Laboratory, Shriners Hospital for Crippled Children, Montreal, Quebec, Canada.
authors.forename: Q
authors.initials: Q
authors.lastname: Nguyen
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: P J
authors.initials: PJ
authors.lastname: Roughley
authors.forename: J S
authors.initials: JS
authors.lastname: Mort
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D001172:Arthritis, Rheumatoid / Q000378:metabolism; D002358:Cartilage, Articular / Q000378:metabolism*; D002401:Cathepsin B / Q000378:metabolism; D056649:Cathepsin G; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism; D002918:Chymotrypsin / Q000378:metabolism; D003546:Cysteine Endopeptidases; D010450:Endopeptidases / Q000378:metabolism*; D016326:Extracellular Matrix Proteins; D006801:Humans; D007231:Infant, Newborn; D019278:Matrix Metalloproteinase 3; D008666:Metalloendopeptidases / Q000378:metabolism; D008875:Middle Aged; D008969:Molecular Sequence Data; D010003:Osteoarthritis / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism*; D012697:Serine Endopeptidases; D000099249:Proteoglycan Link Protein
chemical_list: D002401:Cathepsin B; D056649:Cathepsin G; D056668:Cathepsin L; D002403:Cathepsins; D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; D010450:Endopeptidases; D016326:Extracellular Matrix Proteins; D019278:Matrix Metalloproteinase 3; D008666:Metalloendopeptidases; D010446:Peptide Fragments; D011506:Proteins; D011509:Proteoglycans; D012697:Serine Endopeptidases; D000099249:Proteoglycan Link Protein; C534094:CTSG protein, human; C534281:CTSL protein, human