Hyaluronan (HA) is a high MW glycosaminoglycan significantly involved in the formation and stability of extracellular matrix via its association with specific HA-binding proteins. HAPLN1, also known as CRTL1 (Cartilage Link Protein 1, cLP ) and link protein, is a member of HA-binding protein (hyaladherins) family, and contains a common structural domain of about 100 amino acids that is termed a Link module with two α-helices and two antiparallel β-sheets. HAPLN1/CRTL1 stabilizes the interaction between hyaluronan (HA) and versican, two extracellular matrix components essential for cardiac development. Link module superfamily can be divided into three subgroups, and the HAPLN family are C domain-type proteins that have an extended structure with one N-terminal V-type Ig-like domain followed by two link modules. In cartilage, aggrecan forms - cLP stabilized aggregates with HA that provides the tissue with its load bearing properties. HAPLN1 is a component of follicular matrix, was shown to enhance cumulus-oocyte complex (COC) expansion in vitro. HAPLN1 may promote periovulatory granulosa cell survival, which would facilitate their differentiation into luteal cells.
