Hemopexin is a serum glycoprotein that binds heme and transports it to the liver for breakdown and iron recovery, after which the free hemopexin returns to the circulation. Structurally hemopexin consists of two similar halves of approximately two hundred amino acid residues connected by a histidine-rich hinge region. Each half is itself formed by the repetition of a basic unit of some 35 to 45 residues. Hemopexin-like domains have been found [1,2] in two other types of proteins:

• In vitronectin, a cell adhesion and spreading factor found in plasma and tissues. Vitronectin, like hemopexin, has two hemopexin-like domains.
• In most members of the matrix metalloproteinases family (matrixins) (see <PDOC00129>): MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, MMP-10, MMP-11, MMP-12, MMP-13, MMP-14, MMP-15, MMP-16, MMP-17, MMP-18, MMP-19, MMP-20, MMP-24, and MMP-25. These zinc endoproteases have a single hemopexin-like domain in their C-terminal section.

It is suggested that the hemopexin domain facilitates binding to a variety of molecules and proteins. The signature pattern for this type of domain has been derived from the best conserved region which is located at the beginning of the second repeat.