Proteoglycan 4 (PRG4)

Proteoglycan 4 is an approximately 345-kD proteoglycan specifically synthesized by chondrocytes located at the surface of articular cartilage, and also by some synovial lining cells. This protein contains both chondroitin sulfate and keratan sulfate glycosaminoglycans. The cDNA encodes a protein of 1,404 amino acids with a somatomedin B homology domain, heparin-binding domains, multiple mucin-like repeats, a hemopexin domain, and an aggregation domain. There are 3 consensus sequences for N-glycosylation and 1 chondroitin sulfate substitution site. The locus for autosomal recessive camptodactyly-arthropathy-coxa vara-pericarditis syndrome maps to chromosome 1q25-q31. This protein may act as a joint/intimal cell lubricant, and cell overgrowth may be primary to the pathogenesis of this protein.