Biglycan

Biglycan is a small leucine-rich repeat proteoglycan (SLRP) which is found in a variety of extracellular matrix tissues, including bone, cartilage and tendon.

Composition

It consists of a protein core containing leucine-rich repeat regions and two glycosaminoglycan (GAG) chains consisting of either chondroitin sulfate (CS) or dermatan sulfate (DS), with DS being more abundant in most connective tissues. The CS/DS chains are attached at amino acids 5 and 10 in human biglycan. [Roughley PJ and White RJ (1989) Dermatan sulphate proteoglycans of human articular cartilage. The properties of dermatan sulphate proteoglycans I and II. Biochem J 262:823-827.] The composition of the GAG chains has been reported as varying according to tissue of origin. Non-glycanated forms of biglycan (no GAG chains) increase with age in human articular cartilage. [Roughley PJ et al. (1993) Non-proteoglycan forms of biglycan increase with age in human articular cartilage. Biochem J 295:421-426.]

Nomenclature

The name "biglycan" was proposed in an article by Fisher, Termine and Young in an article in the Journal of Biological Chemistry in 1989 because the proteoglycan contained two GAG chains; formerly it was known as proteoglycan-I (PG-I). [Fisher LW et al. (1989) Deduced protein sequence of bone small proteoglycan I (biglycan) shows homology with proeoglycan II (decorin) and several nonconnective tissue proteins in a variety of species. J Biol Chem 996:43-48.]

Diversity

The structure of biglycan core protein is highly conserved across species; over 90% homology has been reported for rat, mouse, bovine and human biglycan core proteins.

Interactions

Biglycan interacts with collagen, both via the core protein and GAG chains [ Schonherr E et al. (1995) Interaction of biglycan with type I collagen. J Biol Chem. 10;270(6):2776-83. ] [ Pogany G. et al (1994) The in vitro interaction of proteoglycans with type I collagen is modulated by phosphate. Arch Biochem Biophys. 15;313(1):102-11.] . It has been reported that biglycan interacts more strongly with collagen type II than collagen type I [Vynios DH et al. (2001) The interactions of cartilage proteoglycans with collagens are determined by their structures. Biochimie. 83(9):899-906.] [Bidanset D et al. (1992)Binding of the proteoglycan decorin to collagen type VI. J Biol Chem. 15;267(8):5250-6. ] . Biglycan has been reported to compete with decorin for the same binding site on collagen. [ Schonherr E et al. (1995) Interaction of biglycan with type I collagen. J Biol Chem. 10;270(6):2776-83. ]

imilarity to decorin

The composition of GAG chains of biglycan and decorin originating from the same tissue has been reported to be similar [ Cheng F et al. (1994) Patterns of uronosyl epimerization and 4-/6-O-sulphation in chondroitin/dermatan sulphate from decorin and biglycan of various bovine tissues Glycobiology. 4(5):685-96 ] .

Function

Biglycan is believed to play a role in the mineralisation of bone. Knock-out mice that have had the gene for biglycan suppressed have an osteoporosis-like phenotype with reduced growth rate and lower bone mass than mice that can express biglycan. [Xu T et al. (1998) targeted disruption of the biglycan gene leas to an osteoporosis-like phenotype. Nature Genet 20:78-82.]

Biglycan core protein binds to the growth factors BMP-4 and influences its bioactivity. [Moreno M et al. (2005) Biglycan is a new extracellular component of the Chordin-BMP4 signaling pathway. EMBO J. 6;24(7):1397-405.] It has also been reported that the presence of biglycan is necessary for BMP-4 to exert its effects on osteoblasts [ Chen XD et al. (2004) The small leucine-rich proteoglycan biglycan modulates BMP-4-induced osteoblast differentiation. FASEB J. ;18(9):948-58. ] . There is also evidence that biglycan binds to TGF-beta 1

References

External links

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