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Transferrin Edit Wikipedia article
PDB rendering based on 1a8e.
|Symbols||; PRO1557; PRO2086; TFQTL1|
|External IDs||ChEMBL: GeneCards:|
|RNA expression pattern|
Transferrin glycoproteins bind iron tightly, but reversibly. Although iron bound to transferrin is less than 0.1% (4 mg) of total body iron, it forms the most vital iron pool with the highest rate of turnover (25 mg/24 h). Transferrin has a molecular weight of around 80 KDa and contains two specific high-affinity Fe(III) binding sites. The affinity of transferrin for Fe(III) is extremely high (association constant is 1020 M−1 at pH 7.4) but decreases progressively with decreasing pH below neutrality.
When not bound to iron, transferrin is known as "apotransferrin" (see also apoprotein).
When a transferrin protein loaded with iron encounters a transferrin receptor on the surface of a cell (e.g., to erythroid precursors in the bone marrow), it binds to it and, as a consequence, is transported into the cell in a vesicle by receptor-mediated endocytosis. The pH of the vesicle is reduced by hydrogen ion pumps (H+
ATPases) to about 5.5, causing transferrin to release its iron ions. The receptor (with its ligand, transferrin, bound) 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+
In humans, transferrin consists of a polypeptide chain containing 679 amino acids and two carbohydrate chains. The protein is composed of alpha helices and beta sheets that form two domains. The N- and C- terminal sequences are represented by globular lobes and between the two lobes is an iron-binding site.
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 (CO2−
Transferrin also has a transferrin iron-bound receptor; it is a disulfide-linked homodimer. 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 molecules 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.
The liver is the main site of transferrin synthesis but other tissues and organs, including the brain, also produce transferrin. The main role of transferrin is to deliver iron from absorption centers in the duodenum and white blood cell macrophages to all tissues. Transferrin plays a key role in areas where erythropoiesis and active cell division occur. The receptor helps maintain iron homeostasis in the cells by controlling iron concentrations.
Transferrin is also associated with the innate immune system. It is found in the mucosa and binds iron, thus creating an environment low in free iron that impedes bacterial survival in a process called iron withholding. The level of transferrin decreases in inflammation.
Role in disease
An increased plasma transferrin level is often seen in patients suffering from iron deficiency anemia, during pregnancy, and with the use of oral contraceptives, reflecting an increase in transferrin protein expression. As follows, when plasma transferrin levels rise, there is a reciprocal decrease in percent transferrin iron saturation, and a corresponding increase in total iron binding capacity in iron deficient states A decreased plasma transferrin can occur in iron overload diseases and protein malnutrition. An absence of transferrin results from a rare genetic disorder known as atransferrinemia, a condition characterized by anemia and hemosiderosis in the heart and liver that leads to heart failure and many other complications.
The metal-binding properties of transferrin have a great influence on the biochemistry of plutonium in humans.
Transferrin is an acute phase protein and is therefore seen to decrease in inflammation, cancers and certain diseases.
Atransferrinemia is associated with a deficiency in transferrin.
In nephrotic syndrome, urinary loss of transferrin, along with other serum proteins such as thyroxine-binding globulin, gammaglobulin, and anti-thrombin III, can manifest as iron-resistant microcytic anemia.
A high transferrin level may indicate an iron deficiency anemia. Levels of serum iron and total iron binding capacity (TIBC) are used in conjunction with transferrin to specify any abnormality. See interpretation of TIBC.
Members of the family include blood serotransferrin (or siderophilin, usually simply called transferrin); lactotransferrin (lactoferrin); milk transferrin; egg white ovotransferrin (conalbumin); and membrane-associated melanotransferrin.
- Crichton RR, Charloteaux-Wauters M (May 1987). "Iron transport and storage". European Journal of Biochemistry / FEBS 164 (3): 485–506. doi:10.1111/j.1432-1033.1987.tb11155.x. PMID 3032619.
- Yang F, Lum JB, McGill JR, Moore CM, Naylor SL, van Bragt PH, Baldwin WD, Bowman BH (May 1984). "Human transferrin: cDNA characterization and chromosomal localization". Proceedings of the National Academy of Sciences of the United States of America 81 (9): 2752–6. doi:10.1073/pnas.81.9.2752. PMC 345148. PMID 6585826.
- Aisen P, Leibman A, Zweier J (Mar 1978). "Stoichiometric and site characteristics of the binding of iron to human transferrin" (PDF). The Journal of Biological Chemistry 253 (6): 1930–7. PMID 204636.
- "Transferrin Structure". St. Edward's University. 2005-07-18. Retrieved 2009-04-24.
- Macedo MF, de Sousa M (Mar 2008). "Transferrin and the transferrin receptor: of magic bullets and other concerns". Inflammation & Allergy Drug Targets 7 (1): 41–52. doi:10.2174/187152808784165162. PMID 18473900.
- doi:10.1016/S0092-8674(04)00130-8. PMID 14980223.; Cheng Y, Zak O, Aisen P, Harrison SC, Walz T (Feb 2004). "Structure of the human transferrin receptor-transferrin complex". Cell 116 (4): 565–76.
- "Asymmetric binding of transferrin receptor to parvovirus capsids". Proceedings of the National Academy of Sciences of the United States of America 104 (16): 6585–9. doi:10.1073/pnas.0701574104. PMC 1871829. PMID 17420467.; Hafenstein S, Palermo LM, Kostyuchenko VA, Xiao C, Morais MC, Nelson CD, Bowman VD, Battisti AJ, Chipman PR, Parrish CR, Rossmann MG (Apr 2007).
- Ritchie RF, Palomaki GE, Neveux LM, Navolotskaia O, Ledue TB, Craig WY (1999). "Reference distributions for the negative acute-phase serum proteins, albumin, transferrin and transthyretin: a practical, simple and clinically relevant approach in a large cohort". Journal of Clinical Laboratory Analysis 13 (6): 273–9. doi:10.1002/(SICI)1098-2825(1999)13:6<273::AID-JCLA4>3.0.CO;2-X. PMID 10633294.
- Miller JL. Iron Deficiency Anemia: A Common and Curable Disease. Cold Spring Harbor perspectives in medicine. 2013;3(7):10.1101/cshperspect.a011866 a011866. doi:10.1101/cshperspect.a011866.
- Sharpe PC (Nov 2001). "Biochemical detection and monitoring of alcohol abuse and abstinence". Annals of Clinical Biochemistry 38 (Pt 6): 652–64. doi:10.1258/0004563011901064. PMID 11732647.
- Jain S, Gautam V, Naseem S (Jan 2011). "Acute-phase proteins: As diagnostic tool". Journal of Pharmacy & Bioallied Sciences 3 (1): 118–27. doi:10.4103/0975-7406.76489. PMC 3053509. PMID 21430962.
- "Normal Reference Range Table". Interactive Case Study Companion to Pathlogical Basis of Disease. The University of Texas Southwestern Medical Center at Dallas. Retrieved 2008-10-25.
Kumar V, Hagler HK (1999). Interactive Case Study Companion to Robbins Pathologic Basis of Disease (6th Edition (CD-ROM for Windows & Macintosh, Individual) ed.). W B Saunders Co. ISBN 0-7216-8462-9.
- Storch S, Kübler B, Höning S, Ackmann M, Zapf J, Blum W, Braulke T (Dec 2001). "Transferrin binds insulin-like growth factors and affects binding properties of insulin-like growth factor binding protein-3". FEBS Letters 509 (3): 395–8. doi:10.1016/S0014-5793(01)03204-5. PMID 11749962.
- Weinzimer SA, Gibson TB, Collett-Solberg PF, Khare A, Liu B, Cohen P (Apr 2001). "Transferrin is an insulin-like growth factor-binding protein-3 binding protein". The Journal of Clinical Endocrinology and Metabolism 86 (4): 1806–13. doi:10.1210/jcem.86.4.7380. PMID 11297622.
- Hsu SL, Lin YF, Chou CK (Apr 1992). "Transcriptional regulation of transferrin and albumin genes by retinoic acid in human hepatoma cell line Hep3B". The Biochemical Journal 283 (2): 611–5. doi:10.1042/bj2830611. PMC 1131079. PMID 1315521.
- M Ching-Ming Chung (October 1984). "Structure and function of transferrin". Biochemical Education 12 (4): 146–154. doi:10.1016/0307-4412(84)90118-3.
- Hershberger CL, Larson JL, Arnold B, Rosteck PR, Williams P, DeHoff B, Dunn P, O'Neal KL, Riemen MW, Tice PA (Dec 1991). "A cloned gene for human transferrin". Annals of the New York Academy of Sciences 646: 140–54. doi:10.1111/j.1749-6632.1991.tb18573.x. PMID 1809186.
- Bowman BH, Yang FM, Adrian GS (1989). "Transferrin: evolution and genetic regulation of expression". Advances in Genetics. Advances in Genetics 25: 1–38. doi:10.1016/S0065-2660(08)60457-5. ISBN 9780120176250. PMID 3057819.
- Parkkinen J, von Bonsdorff L, Ebeling F, Sahlstedt L (Aug 2002). "Function and therapeutic development of apotransferrin". Vox Sanguinis. 83 Suppl 1 (Suppl 1): 321–6. doi:10.1111/j.1423-0410.2002.tb05327.x. PMID 12617162.
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Transferrin Provide feedback
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Internal database links
|Similarity to PfamA using HHSearch:||Phosphonate-bd|
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR001156
Transferrins are eukaryotic iron-binding glycoproteins that control the level of free iron in biological fluids [PUBMED:3032619]. Evidence suggests that members of the TF family arose from the duplication and fusion of two homologous domains, with each duplicated domain binding one iron atom. Members of the family include blood serotransferrin (siderophilin); milk lactotransferrin (lactoferrin); egg white ovotransferrin (conalbumin); and membrane-associated melanotransferrin. Family members that do not bind iron have also been discovered, including inhibitor of carbonic anhydrase (ICA), which strongly binds to and inhibits certain isoforms of carbonic anhydrase [PUBMED:20572014].
This entry represents the transferrin-like domain, which can be further divided into two subdomains that form a cleft inside of which the iron atom is bound in iron-transporting transferrin [PUBMED:2585506]. The iron-coordinating residues consist of an aspartic acid, two tyrosines and a histidine, as well as an arginine that coordinates a requisite anion. In addition to iron and anion liganding residues, the transferrin-like domain contains conserved cysteine residues involved in disulphide bond formation.
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
The graphic that is shown by default represents the longest sequence with a given architecture. Each row contains the following information:
- the number of sequences which exhibit this architecture
a textual description of the architecture, e.g. Gla, EGF x 2, Trypsin.
This example describes an architecture with one
Gladomain, followed by two consecutive
EGFdomains, and finally a single
- a link to the page in the Pfam site showing information about the sequence that the graphic describes
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Note that you can see the family page for a particular domain by clicking on the graphic. You can also choose to see all sequences which have a given architecture by clicking on the Show link in each row.
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Periplasmic binding proteins (PBPs) consist of two large lobes that close around the bound ligand. This architecture is reiterated in transcriptional regulators, such as the lac repressors. In the process of evolution, genes encoding the PBPs have fused with genes for integral membrane proteins. Thus, diverse mammalian receptors contain extracellular ligand binding domains that are homologous to the PBPs; these include glutamate/glycine-gated ion channels such as the NMDA receptor, G protein-coupled receptors, including metabotropic glutamate, GABA-B, calcium sensing, and pheromone receptors, and atrial natriuretic peptide-guanylate cyclase receptors .
The clan contains the following 25 members:DctP DUF3834 HisG Lig_chan-Glu_bd Lipoprotein_8 Lipoprotein_9 LysR_substrate Mycoplasma_p37 NMT1 NMT1_2 NMT1_3 OpuAC PBP_like PBP_like_2 Phosphonate-bd SBP_bac_1 SBP_bac_11 SBP_bac_3 SBP_bac_5 SBP_bac_6 SBP_bac_8 TctC Transferrin VitK2_biosynth YhfZ_C
We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database (reference proteomes) using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the UniProtKB sequence database, the NCBI sequence database, and our metagenomics sequence database. More...
There are various ways to view or download the sequence alignments that we store. We provide several sequence viewers and a plain-text Stockholm-format file for download.
We make a range of alignments for each Pfam-A family:
- the curated alignment from which the HMM for the family is built
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- Representative Proteomes (RPs) at 15%, 35%, 55% and 75% co-membership thresholds
- alignment generated by searching the UniProtKB sequence database using the family HMM
- alignment generated by searching the NCBI sequence database using the family HMM
- alignment generated by searching the metagenomics sequence database using the family HMM
You can see the alignments as HTML or in three different sequence viewers:
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We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.
1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
Format an alignment
We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.
You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.
HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...
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This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.
Note: You can also download the data file for the tree.
Curation and family details
This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.
|Number in seed:||8|
|Number in full:||839|
|Average length of the domain:||292.60 aa|
|Average identity of full alignment:||32 %|
|Average coverage of the sequence by the domain:||84.93 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 11927849 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||14|
|Download:||download the raw HMM for this family|
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This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the More....
This chart is a modified "sunburst" visualisation of the species tree for this family. It shows each node in the tree as a separate arc, arranged radially with the superkingdoms at the centre and the species arrayed around the outermost ring.
How the sunburst is generated
The tree is built by considering the taxonomic lineage of each sequence that has a match to this family. For each node in the resulting tree, we draw an arc in the sunburst. The radius of the arc, its distance from the root node at the centre of the sunburst, shows the taxonomic level ("superkingdom", "kingdom", etc). The length of the arc represents either the number of sequences represented at a given level, or the number of species that are found beneath the node in the tree. The weighting scheme can be changed using the sunburst controls.
In order to reduce the complexity of the representation, we reduce the number of taxonomic levels that we show. We consider only the following eight major taxonomic levels:
Colouring and labels
Segments of the tree are coloured approximately according to their superkingdom. For example, archeal branches are coloured with shades of orange, eukaryotes in shades of purple, etc. The colour assignments are shown under the sunburst controls. Where space allows, the name of the taxonomic level will be written on the arc itself.
As you move your mouse across the sunburst, the current node will be highlighted. In the top section of the controls panel we show a summary of the lineage of the currently highlighed node. If you pause over an arc, a tooltip will be shown, giving the name of the taxonomic level in the title and a summary of the number of sequences and species below that node in the tree.
Anomalies in the taxonomy tree
There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.
Missing taxonomic levels
Some species in the taxonomic tree may not have one or more of the main eight levels that we display. For example, Bos taurus is not assigned an order in the NCBI taxonomic tree. In such cases we mark the omitted level with, for example, "No order", in both the tooltip and the lineage summary.
Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
So that these nodes are not simply omitted from the sunburst tree, we group them together in a separate branch (or segment of the sunburst tree). Since we cannot determine the lineage for these unmapped species, we show all levels between the superkingdom and the species as "uncategorised".
Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
Too many species/sequences
For large species trees, you may see blank regions in the outer layers of the sunburst. These occur when there are large numbers of arcs to be drawn in a small space. If an arc is less than approximately one pixel wide, it will not be drawn and the space will be left blank. You may still be able to get some information about the species in that region by moving your mouse across the area, but since each arc will be very small, it will be difficult to accurately locate a particular species.
The tree shows the occurrence of this domain across different species. More...
We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.
Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.
If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.
For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.
Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
You can use the tree controls to manipulate how the interactive tree is displayed:
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Please note: for large trees this can take some time. While the tree is loading, you can safely switch away from this tab but if you browse away from the family page entirely, the tree will not be loaded.
There are 12 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Transferrin domain has been found. There are 277 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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