DISTINCT ISOFORMS OF CHICKEN DECORIN CONTAIN EITHER ONE OR 2 DERMATANSULFATE CHAINS

Decorin, a member of a family of proteins with leucine-rich repeat mot ifs, is a widely distributed extracellular matrix proteoglycan that is thought to be responsible for the structure, tissue organization, and surface properties of fibrils. In mammals, decorin carries one chondr oitin/dermatan sulfate chain as a distinction from its homologue, bigl ycan, which contains two glycosaminoglycan chains. With the aim to stu dy decorin-collagen interactions in chicken, where the fibrillar organ ization of cartilage collagens is best understood, we have isolated de corin-related proteoglycans from sternal cartilage of 10-day-old broil er chickens. Small chondroitin/dermatan sulfate proteoglycans were res olved by hydrophobic interaction chromatography into two fractions, DC N I and DCN II. Both forms contained dermatan sulfate and, in addition , keratan sulfate chains. Tryptic fingerprinting revealed that the cor e proteins of DCN I and DCN II were identical. The protein was identif ied as decorin by amino-terminal sequencing. DCN II was found to conta in two dermatan sulfate chains, whereas DCN I had a single dermatan su lfate chain. The dermatan sulfate attachment sites are located near th e NH2 terminus of the core protein, i.e. at Ser-4 and Ser-16 in DCN II and at Ser-4 in DCN I. The keratan sulfate attachment sites are locat ed in the central portion of the core protein, at Asn-179 and Asn-230. The presence of two dermatan sulfate chains renders the chicken prote oglycan DCN II structurally similar to mammalian biglycan. Interesting ly, biglycan has not been detected in chicken. Therefore, in birds, DC N II may function as a biglycan substitute.