Cartilage oligomeric matrix protein and thrombospondin 1

Abstract

Cartilage oligomeric matrix protein (COMP) and thrombospondin 1 (TSP1) were purified in a native form from normal bovine articular cartilage. The key step in the purification scheme was selective extraction with EDTA‐containing buffer. Final separation of these two molecules was achieved by heparin affinity chromatography. Particles viewed by electron microscopy after rotary shadowing and negative staining revealed structures similar to their prototype molecules; from the Swarm rat chondrosarcoma for COMP, or from platelets for TSP1. Attachment of primary bovine chondrocytes to purified matrix proteins was investigated. Cells attached to COMP but not to the structurally related TSP1 indicating separate functions for these proteins in cartilage.

Thrombospondin 1 binds to the surface of bovine articular chondrocytes by a linear RGD‐dependent mechanism

“…Attachment also depended upon the presence of calcium, since removal of calcium from thrombospondin 1 by treatment with EDTA completely inhibited the subsequent attachment of chondroeytes. A recent study [22] reported that bovine cartilage oligomeric protein (COMP) attached to articular cartilage chondrocytes, but that thrombospondin 1 did not. However, it should be noted that the thrombospondin 1 in that study was exposed to EDTA during its isolation, a procedure that irreversibly abolishes its capacity to attach chondrocytes.…”

Disruption of Extracellular Matrix Structure May Cause Pseudoachondroplasia Phenotypes in the Absence of Impaired Cartilage Oligomeric Matrix Protein Secretion

“…Unspecific binding sites were blocked with 1% bovine serum albumin. 5 ϫ 10 4 chondrocytes were incubated for 20 h at 37°C in substrate-coated wells as described earlier (37). Non-attached cells were removed by careful washing with phosphatebuffered saline.…”

Disease-causing Mutations in Cartilage Oligomeric Matrix Protein Cause an Unstructured Ca2+ Binding Domain

“…We refer to the mutation here as deletion of Asp-470 because the net effect of deletion of any one of these 5 Asp residues is removal of the single Asp residue (Asp-470) that separates calcium-binding loops 10 and 11. , and recombinant proteins expressed in bacteria (C). The domain structure of a COMP monomer is based on primary sequence analysis of the thrombospondins, as well as electron microscopy (44), which shows a bouquetlike structure, topped with globular heads. Depiction of the various domains in not meant to infer specific structural conformations.…”