MOLECULAR-CLONING AND TISSUE DISTRIBUTION OF KERATOCAN - BOVINE CORNEAL KERATAN SULFATE PROTEOGLYCAN 37A

Previous studies showed that the keratan sulfate-containing proteoglyc ans of bovine corneal stroma contain three unique core proteins design ated 37A, 37B, and 25 (Funderburgh, J, L,, Funderburgh, M. L., Mann, M , M,, and Conrad, G, W, (1991) J, Biol, Chem, 266, 14226-14231), Degen erate oligonucleotides designed from amino acid sequences of the 37A p rotein were used to screen a cDNA expression library from cultured bov ine keratocytes, A cDNA clone coding for keratocan, a 37A protein, was isolated and sequenced. The deduced keratocan amino acid sequence is unique but related to two other keratan sulfate-containing proteins, l umican (the 37B core protein) and fibromodulin, These three proteins s hare approximately 35% amino acid identity and a number of conserved s tructural features.;Northern hybridization and immunoblotting of tissu e extracts found keratocan distribution to be more limited than that o f lumican or fibromodulin, Keratocan is abundant in cornea and sclera and detected in much lesser amounts in skin, ligament, cartilage, arte ry, and striated muscles, Only in cornea was keratocan found to contai n large, sulfated keratan sulfate chains. Keratocan, like lumican, is a core protein of a major corneal proteoglycan but is present in non-c orneal tissues primarily as a nonsulfated glycoprotein.