Immunoglobulin (Ig)-like domain of chondroitin sulfate proteoglycans (CSPGs), human cartilage link protein (LP), and similar proteins
Ig_CSPGs_LP: immunoglobulin (Ig)-like domain similar to that found in chondroitin sulfate proteoglycans (CSPGs) and human cartilage link protein (LP). Included in this group are the CSPGs aggrecan, versican, and neurocan. In CSPGs, this Ig-like domain is followed by hyaluronan (HA)-binding tandem repeats, and a C-terminal region with epidermal growth factor-like, lectin-like, and complement regulatory protein-like domains. Separating these N- and C-terminal regions is a nonhomologous glycosaminoglycan attachment region. In cartilage, aggrecan forms cartilage link protein stabilized aggregates with hyaluronan (HA). These aggregates contribute to the tissue's load bearing properties. Aggrecan and versican have a wide distribution in connective tissue and extracellular matrices. Neurocan is localized almost exclusively in nervous tissue. Aggregates having other CSPGs substituting for aggrecan may contribute to the structural integrity of many different tissues. There is considerable evidence that HA-binding CSPGs are involved in developmental processes in the central nervous system. Members of the vertebrate HPLN (hyaluronan/HA and proteoglycan binding link) protein family are physically linked adjacent to CSPG genes.