SEQUENCE AND STRUCTURAL IMPLICATIONS OF A BOVINE CORNEAL KERATAN SULFATE PROTEOGLYCAN CORE PROTEIN - PROTEIN-37B REPRESENTS BOVINE LUMICAN AND PROTEIN-37A AND PROTEIN-25 ARE UNIQUE

Amino acid sequence from tryptic peptides of three different bovine co rneal keratan sulfate proteoglycan (KSPG) core proteins (designated 37 A, 37B, and 25) showed similarities to the sequence of a chicken KSPG core protein lumican. Bovine lumican cDNA was isolated from a bovine c orneal expression library by screening with chicken lumican cDNA. The bovine cDNA codes for a 342-amino acid protein, M(r) 38,712, containin g amino acid sequences identified in the 37B KSPG core protein. The bo vine lumican is 68% identical to chicken lumican, with an 83% identity excluding the N-terminal 40 amino acids. Location of 6 cysteine and 4 consensus N-glycosylation sites in the bovine sequence were identical to those in chicken lumican. Bovine lumican had about 50% identity to bovine fibromodulin and 20% identity to bovine decorin and biglycan. About two-thirds of the lumican protein consists of a series of 10 ami no acid leucine-rich repeats that occur in regions of calculated high beta-hydrophobic moment, suggesting that the leucine-rich repeats cont ribute to beta-sheet formation in these proteins. Sequences obtained f rom 37A and 25 core proteins were absent in bovine lumican, thus predi cting a unique primary structure and separate mRNA for each of the thr ee bovine KSPG core proteins.