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Description

Haptoglobin (UniProt: P00738, also known as Zonulin) is encoded by the HP gene (Gene ID: 3240) in human. Haptoglobin is a hemoglobin-binding acute-phase glycoprotein that is synthesized in the liver and is secreted in plasma. Although it belongs to the peptidase S1 family, it does not have any enzymatic activity. It is a tetramer of disulfide-linked two alpha and two beta chains and displays anti-inflammatory and antioxidative properties. It is synthesized with a signal peptide (aa 1-18), which is subsequently cleaved off to generate the mature form that can be further cleaved into an alpha (19-160) and a beta chain (aa 162-406). Haptoglobin complexes with free hemoglobin, resulting from erythrocyte hemolysis, and allows hepatic recycling of heme iron and prevents kidney damage. Hemoglobin/haptoglobin complex is rapidly cleared by the macrophage CD163 scavenger receptor expressed on Kupfer cells through an endocytic lysosomal degradation pathway. Its CD163 interacting region is localized to amino acids 318-323. (Ref.: Schaer, DJ., et al. (2014). Front. Physiol. 5, 415).