Editing Transferrin (section)

== Structure ==

In humans, transferrin consists of a polypeptide chain containing 679 [[amino acids]] and two carbohydrate chains. The protein is composed of [[alpha helix|alpha helices]] and [[beta sheet]]s that form two [[protein domain|domains]].<ref name="stedwards">{{cite web | url = http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Projects04/Transferrin/structure.htm | title = Transferrin Structure | date = 2005-07-18 | publisher = St. Edward's University | access-date = 2009-04-24 | url-status = dead | archive-url = https://archive.today/20121211180614/http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Projects04/Transferrin/structure.htm | archive-date = 2012-12-11 }}</ref> The N- and C- terminal sequences are represented by globular lobes and between the two lobes is an iron-binding site.<ref name="Dewan_1993" />

The [[amino acids]] which bind the iron ion to the transferrin are identical for both lobes; two [[tyrosines]], one [[histidine]], and one [[aspartic acid]]. For the iron ion to bind, an [[anion]] is required, preferably [[carbonate]] ({{chem|CO|3|2−}}).<ref name="stedwards"/><ref name="Baker_1992" />

Transferrin also has a transferrin iron-bound [[receptor (biochemistry)|receptor]]; it is a disulfide-linked [[homodimer]].<ref name="pmid18473900">{{cite journal | vauthors = Macedo MF, de Sousa M | title = Transferrin and the transferrin receptor: of magic bullets and other concerns | journal = Inflammation & Allergy - Drug Targets | volume = 7 | issue = 1 | pages = 41–52 | date = March 2008 | pmid = 18473900 | doi = 10.2174/187152808784165162 }}</ref> In humans, each monomer consists of 760 amino acids. It enables [[ligand]] bonding to the transferrin, as each [[monomer]] can bind to one or two atoms of iron. Each monomer consists of three domains: the protease, the helical, and the apical domains. The shape of a transferrin receptor resembles a butterfly based on the intersection of three clearly shaped domains.<ref name="stedwards"/> Two main transferrin receptors found in humans denoted as transferrin receptor 1 (TfR1) and transferrin receptor 2 (TfR2). Although both are similar in structure, TfR1 can only bind specifically to human TF where TfR2 also has the capability to interact with [[Bovinae|bovine]] TF.<ref name="Kawabata_2019" />

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File:PDB 1suv EBI.jpg|Transferrin bound to its receptor.<ref name="pmid14980223">{{PDB|1suv}}; {{cite journal | vauthors = Cheng Y, Zak O, Aisen P, Harrison SC, Walz T | title = Structure of the human transferrin receptor-transferrin complex | journal = Cell | volume = 116 | issue = 4 | pages = 565–76 | date = Feb 2004 | pmid = 14980223 | doi = 10.1016/S0092-8674(04)00130-8 | s2cid = 2981917 }}</ref>
File:PDB 2nsu EBI.jpg|Transferrin receptor complex.<ref name="pmid17420467">{{PDB|2nsu}}; {{cite journal | vauthors = Hafenstein S, Palermo LM, Kostyuchenko VA, Xiao C, Morais MC, Nelson CD, Bowman VD, Battisti AJ, Chipman PR, Parrish CR, Rossmann MG | title = Asymmetric binding of transferrin receptor to parvovirus capsids | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 16 | pages = 6585–9 | date = Apr 2007 | pmid = 17420467 | pmc = 1871829 | doi = 10.1073/pnas.0701574104 | bibcode = 2007PNAS..104.6585H | doi-access = free }}</ref>
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