Characterization of the tissue-specific proteoglycans synthesized by chondrocytes from nanomelic chick embryos

Cartilage from the avian mutant nanomelia has been reported to synthesize cartilage-specific proteoglycans, PGS(SC)-I, at 1-2% of normal values [McKeown & Goetinck (1979) Dev. Biol. 71, 203-215]. Proteoglycans were endogenously labelled with [35S]sulphate and extracted from cartilage in 4 M-guanidine hydrochloride and chromatographed on controlled-pore glass 1400. PGS(SC)-I was obtained from the void volume of these columns. Dissociative sucrose-density-gradient analysis revealed a greater than normal polydispersity in the nanomelic PGS(SC)-I. Fractions from both the controlled-pore glass 1400 void volume and sucrose gradients were tested for their ability to bind specific antibody against cartilage proteoglycan monomer. In all instances, binding of normal fractions was greater than 90%, whereas binding to nanomelic fractions ranged from 20 to 65%. Chromatography of PGS(SC)-I on controlled-pore glass 2500 resulted in 70% of the normal and 25% of the mutant proteoglycans eluting as aggregates. Chondroitin sulphate chains from mutant PGS(SC)-I appeared slightly larger than normal when chromatographed on controlled-pore glass 500. In addition, PGS(SC)-I from nanomelic cartilage is more susceptible to proteolysis in vitro than the PGS(SC)-I from normal cartilage. This evidence suggests that the small amount of cartilage-specific proteoglycan synthesized by nanomelic cartilage is not normal.