Hemopexin (EC3.2.1.35) is a serum glycoprotein that binds haem and transports it to the liver for breakdown and iron recovery, after which the free hemopexin returns to the circulation.[2] Hemopexin prevents haem-mediated oxidative stress. 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 in two other types of proteins, vitronectin,[3] a cell adhesion and spreading factor found in plasma and tissues, and matrixins MMP-1, MMP-2, MMP-3, MMP-9, MMP-10, MMP-11, MMP-12, MMP-14, MMP-15 and MMP-16, members of the matrix metalloproteinase family that cleave extracellular matrix constituents.[4] These zinc endopeptidases, which belong to MEROPS peptidase subfamily M10A, 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, for example the HX repeats of some matrixins bind tissue inhibitor of metallopeptidases (TIMPs).
Examples
Human gene encoding proteins containing hemopexin-like repeats include:
HPX (hemopexin, the founding member of this protein family)
^Kojima K, Ogawa H, Matsumoto I, Yoneda A (1998). "Characterization of the ligand binding activities of vitronectin: interaction of vitronectin with lipids and identification of the binding domains for various ligands using recombinant domains". Biochemistry. 37 (18): 6351–6360. doi:10.1021/bi972247n. PMID9572850.
^Das S, Mandal M, Chakraborti T, Mandal A, Chakraborti S (2003). "Structure and evolutionary aspects of matrix metalloproteinases: a brief overview". Mol. Cell. Biochem. 253 (1–2): 31–40. doi:10.1023/A:1026093016148. PMID14619953.
