Tendon extracellular matrix contains pentameric thrombospondin‐4 (TSP‐4)

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Abstract
In preparations of cartilage oligomeric matrix protein (COMP) from bovine tendon two contaminating polypeptides of 120 and 135 kDa were detected. N‐Terminal protein sequencing of these polypeptides showed homology to the N‐terminus and to an internal sequence in TSP‐4, respectively. TSP‐4 was further enriched by heparin affinity chromatography. Electron microscopy of this sample shows primarily five armed particles with globular domains at the periphery connected to a central assembly domain in which smaller N‐terminal globular domains can be resolved tightly packed at the center of the particle. We can thereby confirm the pentameric model for TSP‐4 proposed by Lawler et al. [(1995) J. Biol. Chem. 270, 2809–2814], on the basis of recombinantly expressed protein. We further show that TSP‐4 is abundant in tendon.