Core protein domains of aggrecan. Upper panel: The domains of the aggrecan core protein are depicted. G1, G2 and G3, globular regions; IGD, interglobular domain; KS, keratan sulfate-rich domain; CS1 and CS2, chondroitin sulfate-rich domains. The globular regions are divided into their disulfide-bonded domains. A, link protein-binding domain; B and B′, hyaluronan-binding domains for G1 and homology domains for G2; E, epidermal growth factor-like domains; L, lectin-like domain; C, complement regulatory protein-like domain. Lower panel: The coding exon arrangement of the human aggrecan gene is depicted and the regions of the core protein encoded by each exon is indicated.