Transferrin

Transferrin
PDB rendering based on 1a8e.
Available structures: 1a8e, 1a8f, 1b3e, 1bp5, 1btj, 1d3k, 1d4n, 1dtg, 1fqe, 1fqf, 1jqf, 1n7w, 1n7x, 1n84, 1oqg, 1oqh, 1ryo, 1suv, 2hau, 2hav, 2o7u, 2o84
Identifiers
Symbol(s)	TF; DKFZp781D0156; PRO1557; PRO2086
External IDs	OMIM: 190000 MGI: 98821 Homologene: 68153
Gene Ontology Molecular Function: • ferric iron binding • metal ion binding Cellular Component: • extracellular region • endosome • endocytic vesicle Biological Process: • ion transport • iron ion transport • cellular iron ion homeostasis
RNA expression pattern
More reference expression data
Orthologs
	Human	Mouse
Entrez	7018	22041
Ensembl	ENSG00000091513	ENSMUSG00000032554
Uniprot	P02787	Q3UBW7
Refseq	NM_001063 (mRNA) NP_001054 (protein)	NM_133977 (mRNA) NP_598738 (protein)
Location	Chr 3: 134.95 - 134.98 Mb	Chr 9: 103.07 - 103.09 Mb
Pubmed search	[1]	[2]

Transferrin is a blood plasma protein for iron ion delivery. Transferrin is a glycoprotein, which binds iron very tightly but reversibly. Although iron bound to transferrin is less than 0.1% (4 mg) of the total body iron, dynamically it is the most important iron pool, with the highest rate of turnover (25 mg/24 h). Transferrin has a molecular weight of around 80 kiloDaltons and contains 2 specific high affinity Fe(III) binding sites. The affinity of transferrin for Fe(III) is extremely high (10^23 M^-1 at pH 7.4) but decreases progressively with decreasing pH below neutrality.

When not bound to iron, it is known as "apotransferrin" (see also apoprotein).

Transport mechanism

When a transferrin protein loaded with iron encounters a transferrin receptor on the surface of a cell (importantly, to erythroid precursors in the bone marrow), it binds to it and is consequently transported into the cell in a vesicle. The H⁺ ATPase of the cell will decrease the pH of the vesicle, causing transferrin to release its iron ions. The receptor with its ligand bound to it is then transported through the endocytic cycle back to the cell surface, ready for another round of iron uptake. Each transferrin molecule has the ability to carry two iron ions in the ferric form (Fe3+).

The gene coding for transferrin in humans is located in chromosome band 3q21. Research on king snakes by Dessauer and Zwiefel in 1981 revealed the the inheritance of transferrin is a codominant trait.

Transferrin levels may be checked in iron deficiency, hemochromatosis and other iron overload disorders.

Immune system

Transferrin is also associated with the innate immune system. Transferrin is found in the mucosa and binds iron, thus creating an environment low in free iron, where few bacteria are able to survive.

A decrease in the amount of transferrin would result in hemosiderin in the liver.

Other effects

The metal binding properties of transferrin have a great influence on the biochemistry of plutonium in humans. Transferrin has a bacteriocidal effect on bacteria, in that it makes Fe3+ unavailable to the bacteria.

Pathology

A deficiency is associated with atransferrinemia.

See also

• Beta-2 transferrin
• Transferrin receptor
• Total iron-binding capacity
• Transferrin saturation

External links

• MeSH Transferrin

References

Further reading

• Hershberger CL, Larson JL, Arnold B, et al. (1992). "A cloned gene for human transferrin.". Ann. N. Y. Acad. Sci. 646: 140-54. PMID 1809186. 
• Bowman BH, Yang FM, Adrian GS (1989). "Transferrin: evolution and genetic regulation of expression.". Adv. Genet. 25: 1-38. PMID 3057819. 
• Parkkinen J, von Bonsdorff L, Ebeling F, Sahlstedt L (2003). "Function and therapeutic development of apotransferrin.". Vox Sang. 83 Suppl 1: 321-6. PMID 12617162. 

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