CPG4 is a domain family found in nematodes of one of nine core chondroitin proteoglycans. Vertebrates produce multiple chondroitin sulfate proteoglycans that play important roles in development and tissue mechanics. In the nematode Caenorhabditis elegans, the chondroitin chains lack sulfate but nevertheless play essential roles in embryonic development and vulval morphogenesis. CPG4 has the largest predicted mass of the C. elegans CPGs at 84 kDa. The majority of its 35 predicted glycosaminoglycan attachment sites reside in the COOH-terminal half of the protein, of which four sites were confirmed by DTT modification. The family is rich in conserved cysteines.