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haptoglobin; contains: haptoglobin alpha chain; haptoglobin beta chain (HP)
Function:
- irreversibly binds alpha chain of free oxyhemoglobin
- prevents loss of iron through the kidneys & protects the kidneys from damage by hemoglobin, while making the hemoglobin accessible to degradative enzymes
- tetramer of two alpha & two beta chains formed from common precursor
- may form multimers of MW up to 1000 kD.
- normally accounts for 25% of the alpha-2 band on serum protein electrophoresis (SPE)
- an elevated haptoglobin is the most common abnormality seen on SPE
- haptoglobin is an acute phase reactant & becomes elevated non-specifically in the presence of inflammation or tissue injury
- depressed haptoglobin levels are seen in association with hemolysis
Structure:
- belongs to the peptidase S1 family
- contains 1 peptidase S1 domain
- contains 2 Sushi (CCP/SCR) domains
Compartment: secreted
Expression:
- expressed by the liver & secreted in plasma
Polymorphism:
- in human populations there are two major allelic forms, alpha-1 with 83 residues & alpha-2 with 142 residues
- these alleles determine the 3 major phenotypes HP*1F/HP*1S & HP*2FS
- the two main alleles of HP*1 are called HP*1F (fast) & HP*1S (slow)
Note:
- although homologous to serine proteases, it has lost all essential catalytic residues & has no enzymatic activity
Related
haptoglobin (HP) gene
haptoglobin genotyping
haptoglobin in serum
haptoglobin-related protein (HPR)
General
acute phase protein
alpha 2 globulin
mucoprotein
multisubunit protein
Properties
SIZE: entity length = 406 aa
MW = 45 kD
COMPARTMENT: plasma
MOTIF: signal sequence {1-18}
Sushi domain {31-88}
MOTIF: cysteine residue {C33}
MODIFICATION: cysteine residue {C-INTERCHAIN}
cysteine residue {C52}
MODIFICATION: cysteine residue {C86}
cysteine residue {C86}
MODIFICATION: cysteine residue {C52}
Sushi domain {90-147}
MOTIF: cysteine residue {C92}
MODIFICATION: cysteine residue {C-INTERCHAIN}
cysteine residue {C111}
MODIFICATION: cysteine residue {C145}
cysteine residue {C145}
MODIFICATION: cysteine residue {C111}
cysteine residue {C149}
MODIFICATION: cysteine residue {C-INTERCHAIN}
S1 domain {162-404}
MOTIF: N-glycosylation site {N184}
N-glycosylation site {N207}
N-glycosylation site {N211}
N-glycosylation site {N241}
cysteine residue {C309}
MODIFICATION: cysteine residue {C340}
cysteine residue {C340}
MODIFICATION: cysteine residue {C309}
cysteine residue {C351}
MODIFICATION: cysteine residue {C381}
cysteine residue {C381}
MODIFICATION: cysteine residue {C351}
GENE: haptoglobin gene
MISC-INFO: CONCENTRATION 40-290 MG/DL
Database Correlations
OMIM 140100
MORBIDMAP 140100
UniProt P00738
Pfam PF00089
Entrez Gene 3240
Kegg hsa:3240
References
- Tietz Fundamentals of Clinical Chemistry 3rd ed, WB
Saunders, 1987 pg 331
- Clinical Diagnosis & Management by Laboratory Methods,
J.B. Henry (ed), W.B. Saunders Co., Philadelphia,
PA. 1991, pg 222
- UniProt :accession P00738
- GeneReviews
http://www.ncbi.nlm.nih.gov/sites/genetests/lab/gene/HP
- SHMPD; Singapore Human Mutation and Polymorphism Database
http://shmpd.bii.a-star.edu.sg/gene.php?genestart=A&genename=HP
- Wikipedia; Note: haptoglobin entry
http://en.wikipedia.org/wiki/haptoglobin