title: Link peptide cartilage growth factor is degraded by membrane proteinases.
abstract: The peptide DHLSDNYTLDHDRAIH (Link N), cleaved from the N-terminus of the link protein component of cartilage proteoglycan aggregates by the action of stromelysin, can act as a growth factor and stimulate synthesis of proteoglycans and collagen in articular cartilage [McKenna, Liu, Sansom and Dean (1998) Arthritis Rheum. 41, 157-161]. The mechanism by which this biologically active peptide is degraded and inactivated was investigated using U937 monocytes as a model cell. Time-course experiments showed that two major proteases, an initial serine proteinase followed by a metalloproteinase, acted in sequence. Analysis of the resulting fragments showed that the serine endopeptidase cleavage was at the Leu(3)-Ser(4) bond to produce the peptide SDNYTLDHDRAIH. The terminal serine could then be removed from the resulting peptide by an aminopeptidase. A second metallopeptidase liberated the peptides SDNYTL or DNYTL from DHDRAIH by cleavage at the Leu(9)-Asp(10) bond. The DNYTL peptide intermediate was degraded too rapidly to allow sequencing and sequential aminopeptidase cleavages removed further amino acids from the N-terminus of the remaining DHDRAIH peptide. The identical patterns of breakdown that occurred when either whole cells or purified plasma membranes were used indicated that proteolysis and inactivation of Link N was carried out entirely by membrane-associated enzymes.
authors.affiliation: Department of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Royal College Street, London NW1 0TU, UK. mdean@rvc.ac.uk
authors.forename: M F
authors.initials: MF
authors.lastname: Dean
authors.forename: P
authors.initials: P
authors.lastname: Sansom
mesh_terms: D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D016326:Extracellular Matrix Proteins; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D010447:Peptide Hydrolases; D011506:Proteins / Q000378:metabolism*; D011509:Proteoglycans; D020298:U937 Cells; D000099249:Proteoglycan Link Protein
chemical_list: D010450:Endopeptidases; D016326:Extracellular Matrix Proteins; D008565:Membrane Proteins; D010446:Peptide Fragments; D010447:Peptide Hydrolases; D011506:Proteins; D011509:Proteoglycans; D000099249:Proteoglycan Link Protein