Link domain

A Link domain or Link module, also known as Xlink domain (X for extracellular), is a protein domain that binds to hyaluronic acid.^[1] It is important in blood cell migration and apoptosis.^[2] The link domain is found in some extracellular proteins in vertebrates such as the hyalectans.^[3] It appears to be involved in extracellular matrix assembly and stability, cell adhesion, and migration.^[3][4]

Link domain
Structure of the hyaluronan-binding domain of human CD44
Identifiers
Symbol	LINK
Pfam	PF00193
Pfam clan	CL0056
InterPro	IPR000538
SMART	SM00445
PROSITE	PDOC00955
SCOP2	1o7b / SCOPe / SUPFAM
CDD	cd01102
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Structure

The structure has been shown to consist of two alpha helices and two antiparallel beta sheets arranged around a large hydrophobic core similar to that of C-type lectin.^[5] This domain contains four conserved cysteines involved in two disulphide bonds. The link domain has also been termed HABM (hyaluronic acid binding module)^[4] and PTR (proteoglycan tandem repeat).^[6]

Link domain proteins

Proteins which contain the link domain include:

• the hyalectans (a family of proteoglycans): aggrecan, brevican, neurocan and versican, which are expressed in the CNS;
• the cartilage link protein (LP), a proteoglycan that together with HA and aggrecan forms multimolecular aggregates;
• Tumour necrosis factor-inducible protein 6 (TSG-6), which may be involved in cell-cell and cell-matrix interactions during inflammation and tumourigenesis;
• CD44 antigen, the main cell surface receptor for HA.

See also

• Hyaladherin