Haptoglobin (HP) Human Plasma Native Protein

This gene encodes a preproprotein, which is processed to yield both alpha and beta chains, which subsequently combine as a tetramer to produce haptoglobin. Haptoglobin functions to bind free plasma hemoglobin, which allows degradative enzymes to gain access to the hemoglobin, while at the same time preventing loss of iron through the kidneys and protecting the kidneys from damage by hemoglobin. Mutations in this gene and/or its regulatory regions cause ahaptoglobinemia or hypohaptoglobinemia. This gene has also been linked to diabetic nephropathy, the incidence of coronary artery disease in type 1 diabetes, Crohn's disease, inflammatory disease behavior, primary sclerosing cholangitis, susceptibility to idiopathic Parkinson's disease, and a reduced incidence of Plasmodium falciparum malaria. A similar duplicated gene is located next to this gene on chromosome 16. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq]

Function: Haptoglobin combines with free plasma hemoglobin, preventing loss of iron through the kidneys and protecting the kidneys from damage by hemoglobin, while making the hemoglobin accessible to degradative enzymes.

Subunit structure: Tetramer of two alpha and two beta chains.

Subcellular location: Secreted.

Tissue specificity: Expressed by the liver and secreted in plasma.

Polymorphism: In the human populations there are two major allelic forms, alpha-1 with 83 residues and alpha-2 with 142 residues. These alleles determine the 3 major phenotypes HP*1F/HP*1S and HP*2FS. The two main alleles of HP*1 are called HP*1F (fast) and HP*1S (slow).

Sequence similarities: Belongs to the peptidase S1 family.Contains 1 peptidase S1 domain.Contains 2 Sushi (CCP/SCR) domains.

Caution: Although homologous to serine proteases, it has lost all essential catalytic residues and has no enzymatic activity.