Summary: PDGF/VEGF domain
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Platelet-derived growth factor Edit Wikipedia article
|Platelet-derived growth factor (PDGF)|
Platelet-derived growth factor (PDGF) is one of the numerous growth factors, or proteins that regulate cell growth and division. In particular, it plays a significant role in blood vessel formation (angiogenesis), the growth of blood vessels from already-existing blood vessel tissue. Uncontrolled angiogenesis is a characteristic of cancer. In chemical terms, platelet-derived growth factor is a dimeric glycoprotein composed of two A (-AA) or two B (-BB) chains or a combination of the two (-AB).
PDGF is a potent mitogen for cells of mesenchymal origin, including smooth muscle cells and glial cells. In both mouse and human, the PDGF signalling network consists of four ligands, PDGFA-D, and two receptors, PDGFRalpha and PDGFRbeta. All PDGFs function as secreted, disulphide-linked homodimers, but only PDGFA and B can form functional heterodimers.
Though it is synthesized, stored (in the alpha granules of platelets), and released by platelets upon activation, it is also produced by a plethora of cells including smooth muscle cells, activated macrophages, and endothelial cells
There are five different isoforms of PDGF that activate cellular response through two different receptors. Known ligands include A (PDGFA), B (PDGFB), C (PDGFC), and D (PDGFD), and an AB heterodimer and receptors alpha (PDGFRA) and beta (PDGFRB). PDGF has few other members of the family, for example VEGF sub-family.
The receptor for PDGF, PDGFR is classified as a receptor tyrosine kinase (RTK), a type of cell surface receptor. Two types of PDGFRs have been identified: alpha-type and beta-type PDGFRs. The alpha type binds to PDGF-AA, PDGF-BB and PDGF-AB, whereas the beta type PDGFR binds with high affinity to PDGF-BB and PDGF-AB. PDGF binds to PDGFRs ligand binding pocket located within the second and third immunoglobulin domains. Upon activation by PDGF, these receptors dimerise, and are "switched on" by auto-phosphorylation of several sites on their cytosolic domains, which serve to mediate binding of cofactors and subsequently activate signal transduction, for example, through the PI3K pathway or through reactive oxygen species (ROS)-mediated activation of the STAT3 pathway. Downstream effects of this include regulation of gene expression and the cell cycle. The role of PI3K has been investigated by several laboratories. Accumulating data suggests that, while this molecule is, in general, part of growth signaling complex, it plays a more profound role in controlling cell migration. The different ligand isoforms have variable affinities for the receptor isoforms, and the receptor isoforms may variably form hetero- or homo- dimers. This leads to specificity of downstream signaling. It has been shown that the sis oncogene is derived from the PDGF B-chain gene. PDGF-BB is the highest-affinity ligand for the PDGFR-beta; PDGFR-beta is a key marker of hepatic stellate cell activation in the process of fibrogenesis.
PDGFs are mitogenic during early developmental stages,driving the proliferation of undifferentiated mesenchyme and some progenitor populations. During later maturation stages, PDGF signalling has been implicated in tissue remodelling and cellular differentiation, and in inductive events involved in patterning and morphogenesis.In addition to driving mesenchymal proliferation, PDGFs have been shown to direct the migration, differentiation and function of a variety of specialised mesenchymal and migratory cell types, both during development and in the adult animal. Other growth factors in this family include vascular endothelial growth factors B and C (VEGF-B, VEGF-C) which are active in angiogenesis and endothelial cell growth, and placenta growth factor (PlGF) which is also active in angiogenesis.
PDGF plays a role in embryonic development, cell proliferation, cell migration, and angiogenesis. Over-expression of PDGF has been linked to several diseases such as atherosclerosis, fibrotic disorders and malignancies. Synthesis occurs due to external stimuli such as thrombin, low oxygen tension, or other cytokines and growth factors.
PDGF is a required element in cellular division for fibroblasts, a type of connective tissue cell that is especially prevalent in wound healing. In essence, the PDGFs allow a cell to skip the G1 checkpoints in order to divide. It has been shown that in monocytes-macrophages and fibroblasts, exogenously administered PDGF stimulates chemotaxis, proliferation, and gene expression and significantly augmented the influx of inflammatory cells and fibroblasts, accelerating extracellular matrix and collagen formation and thus reducing the time for the healing process to occur.
In terms of osteogenic differentiation of mesenchymal stem cells, comparing PDGF to epidermal growth factor (EGF), which is also implicated in stimulating cell growth, proliferation, and differentiation, MSCs were shown to have stronger osteogenic differentiation into bone-forming cells when stimulated by epidermal growth factor (EGF) versus PDGF. However, comparing the signaling pathways between them reveals that the PI3K pathway is exclusively activated by PDGF, with EGF having no effect. Chemically inhibiting the PI3K pathway in PDGF-stimulated cells negates the differential effect between the two growth factors, and actually gives PDGF an edge in osteogenic differentiation. Wortmannin is a PI3K-specific inhibitor, and treatment of cells with Wortmannin in combination with PDGF resulted in enhanced osteoblast differentiation compared to just PDGF alone, as well as compared to EGF. These results indicate that the addition of Wortmannin can significantly increase the response of cells into an osteogenic lineage in the presence of PDGF, and thus might reduce the need for higher concentrations of PDGF or other growth factors, making PDGF a more viable growth factor for osteogenic differentiation than other, more expensive growth factors currently used in the field such as BMP2.
PDGF is also known to maintain proliferation of oligodendrocyte progenitor cells. It has also been shown that fibroblast growth factor (FGF) activates a signaling pathway that positively regulates the PDGF receptors in oligodendrocyte progenitor cells.
Like many other growth factors that have been linked to disease, PDGF and its receptors have provided a market for receptor antagonists to treat disease. Such antagonists include (but are not limited to) specific antibodies that target the molecule of interest, which act only in a neutralizing manner.
Age related downregulation of the PDGF receptor on islet beta cells has been demonstrated to prevent islet beta cell proliferation in both animal and human cells and its re-expression triggered beta cell proliferation and corrected glucose regulation via insulin secretion.
A non-viral PDGF "bio patch" can regenerate missing or damaged bone by delivering DNA in a nano-sized particle directly into cells via genes. Repairing bone fractures, fixing craniofacial defects and improving dental implants are among potential uses. The patch employs a collagen platform seeded with particles containing the genes needed for producing bone. In experiments, it new bone fully covered skull wounds in test animals and stimulated growth in human bone marrow stromal cells.
Human genes encoding proteins that belong to the platelet-derived growth factor family include:
- Platelet-activating factor
- Platelet-derived growth factor receptor
- atheroma platelet involvement in smooth muscle proliferation
- Withaferin A potent inhibitor of angiogenesis
- Hannink M, Donoghue DJ (1989). "Structure and function of platelet-derived growth factor (PDGF) and related proteins". Biochim. Biophys. Acta 989 (1): 1–10. doi:10.1016/0304-419x(89)90031-0. PMID 2546599.
- Heldin CH (1992). "Structural and functional studies on platelet-derived growth factor". EMBO J. 11 (12): 4251–4259. PMC 556997. PMID 1425569.
- Minarcik, John. "Global Path Course: Video". Retrieved 2011-06-27.
- "The Basic Biology of Platelet Growth Factors". Retrieved 2014-05-08.
- Kumar, Vinay (2010). Robbins and Coltran Pathologic Basis of Disease. China: Elsevier. pp. 88–89. ISBN 978-1-4160-3121-5.
- Matsui T, Heidaran M, Miki T, Popescu N, La Rochelle W, Kraus M, Pierce J, Aaronson S (1989). "Isolation of a novel receptor cDNA establishes the existence of two PDGF receptor genes". Science 243 (4892): 800–4. doi:10.1126/science.2536956. PMID 2536956.
- Heidaran MA, Pierce JH, Yu JC, Lombardi D, Artrip JE, Fleming TP, Thomason A, Aaronson SA (25 October 1991). "Role of alpha beta receptor heterodimer formation in beta platelet-derived growth factor (PDGF) receptor activation by PDGF-AB". J. Biol. Chem. 266 (30): 20232–7. PMID 1657917.
- Heidaran MA, Pierce JH, Jensen RA, Matsui T, Aaronson SA (5 November 1990). "Chimeric alpha- and beta-platelet-derived growth factor (PDGF) receptors define three immunoglobulin-like domains of the alpha-PDGF receptor that determine PDGF-AA binding specificity". J. Biol. Chem. 265 (31): 18741–4. PMID 2172231.
- Blazevic T, Schwaiberger AV, Schreiner CE, Schachner D, Schaible AM, Grojer CS, Atanasov AG, Werz O, Dirsch VM, Heiss EH (December 2013). "12/15-Lipoxygenase Contributes to Platelet-derived Growth Factor-induced Activation of Signal Transducer and Activator of Transcription 3". J. Biol. Chem. 288 (49): 35592–603. doi:10.1074/jbc.M113.489013. PMC 3853304. PMID 24165129.
- Yu JC, Li W, Wang LM, Uren A, Pierce JH, Heidaran MA (1995). "Differential requirement of a motif within the carboxyl-terminal domain of alpha-platelet-derived growth factor (alpha PDGF) receptor for PDGF focus forming activity chemotaxis, or growth". J. Biol. Chem. 270 (13): 7033–6. doi:10.1074/jbc.270.13.7033. PMID 7706238.
- Hoch RV, Soriano P (2003). "Roles of PDGF in animal development". Development 130 (20): 4769–4784. doi:10.1242/dev.00721. PMID 12952899.
- Olofsson B, Pajusola K, Kaipainen A, von Euler G, Joukov V, Saksela O, Orpana A, Pettersson RF, Alitalo K, Eriksson U (1996). "Vascular endothelial growth factor B, a novel growth factor for endothelial cells". Proc. Natl. Acad. Sci. U.S.A. 93 (6): 2567–2581. doi:10.1073/pnas.93.6.2576. PMC 39839. PMID 8637916.
- Joukov V, Pajusola K, Kaipainen A, Chilov D, Lahtinen I, Kukk E, Saksela O, Kalkkinen N, Alitalo K (1996). "A novel vascular endothelial growth factor, VEGF-C, is a ligand for the Flt4 (VEGFR-3) and KDR (VEGFR-2) receptor tyrosine kinases". EMBO J. 15 (2): 290–298. PMC 449944. PMID 8617204.
- Maglione D, Guerriero V, Viglietto G, Ferraro MG, Aprelikova O, Alitalo K, Del Vecchio S, Lei KJ, Chou JY, Persico MG (1993). "Two alternative mRNAs coding for the angiogenic factor, placenta growth factor (PlGF), are transcribed from a single gene of chromosome 14". Oncogene 8 (4): 925–931. PMID 7681160.
- "PDGF Pathways". Retrieved 2007-11-17.
- Alvarez RH, Kantarjian HM, Cortes JE (September 2006). "Biology of platelet-derived growth factor and its involvement in disease". Mayo Clin. Proc. 81 (9): 1241–57. doi:10.4065/81.9.1241. PMID 16970222.
- Song G, Ouyang G, Bao S (2005). "The activation of Akt/PKB signaling pathway and cell survival". J. Cell. Mol. Med. 9 (1): 59–71. doi:10.1111/j.1582-4934.2005.tb00337.x. PMID 15784165.
- Pierce GF, Mustoe TA, Altrock BW, Deuel TF, Thomason A (April 1991). "Role of platelet-derived growth factor in wound healing". J. Cell. Biochem. 45 (4): 319–26. doi:10.1002/jcb.240450403. PMID 2045423.
- Kratchmarova I, Blagoev B, Haack-Sorensen M, Kassem M, Mann M (June 2005). "Mechanism of divergent growth factor effects in mesenchymal stem cell differentiation". Science 308 (5727): 1472–7. doi:10.1126/science.1107627. PMID 15933201.
- Hayashi, A. The New Standard of Care for Nonunions?. AAOS Now. 2009.
- Barres BA, Hart IK, Coles HS, Burne JF, Voyvodic JT, Richardson WD, Raff MC (1992). "Cell Death and Control of Cell Survival in the Oligodendrocyte Lineage". Cell 70 (1): 31–46. doi:10.1016/0092-8674(92)90531-G. PMID 1623522.
- Proto-Oncogene Proteins c-sis at the US National Library of Medicine Medical Subject Headings (MeSH)
- McKinnon RD, Matsui T, Dubois-Dalcq M, Aaronson SA (November 1990). "FGF modulates the PDGF-driven pathway of oligodendrocyte development". Neuron 5 (5): 603–14. doi:10.1016/0896-6273(90)90215-2. PMID 2171589.
- Paul D, Lipton A, Klinger I (1971). "Serum factor requirements of normal and simian virus 40-transformed 3T3 mouse fibroplasts". Proc Natl Acad Sci U S A. 68 (3): 645–52. doi:10.1073/pnas.68.3.645. PMC 389008. PMID 5276775.
- Friedlaender GE et al. The Role of Recombinant Human Platelet-derived Growth Factor-BB (rhPDGF-BB) in Orthopaedic Bone Repair and Regeneration Curr Pharm Des. 2013;19(19):3384-90. PMID 23432673. Quote: "Demonstration of the safety and efficacy of rhPDGF-BB in the healing of chronic foot ulcers in diabetic patients and regeneration of alveolar (jaw) bone lost due to chronic infection from periodontal disease has resulted in two FDA-approved products based on this molecule"
- Shulman T, Sauer FG, Jackman RM, Chang CN, Landolfi NF (July 1997). "An antibody reactive with domain 4 of the platelet-derived growth factor beta receptor allows BB binding while inhibiting proliferation by impairing receptor dimerization". J. Biol. Chem. 272 (28): 17400–4. doi:10.1074/jbc.272.28.17400. PMID 9211881.
- McClintock JT, Chan IJ, Thaker SR, Katial A, Taub FE, Aotaki-Keen AE, Hjelmeland LM (1992). "Detection of c-sis proto-oncogene transcripts by direct enzyme-labeled cDNA probes and in situ hybridization". In Vitro Cell Dev Biol 28A (2): 102–8. doi:10.1007/BF02631013. PMID 1537750.
- "Researchers make older beta cells act young again". Eurekalert.org. 2011-10-12. Retrieved 2013-12-28.
- "New Stanford molecular target for diabetes treatment discovered - Office of Communications & Public Affairs - Stanford University School of Medicine". Med.stanford.edu. 2011-10-12. Retrieved 2013-12-28.
- "Bio patch can regrow bone for dental implants and craniofacial defects". KurzweilAI. 2013-11-12. doi:10.1016/j.biomaterials.2013.10.021. Retrieved 2013-12-28.
- Elangovan S, D'Mello SR, Hong L, Ross RD, Allamargot C, Dawson DV, Stanford CM, Johnson GK, Sumner DR, Salem AK (2014). "The enhancement of bone regeneration by gene activated matrix encoding for platelet derived growth factor". Biomaterials 35 (2): 737–747. doi:10.1016/j.biomaterials.2013.10.021. PMC 3855224. PMID 24161167.
- platelet-derived growth factor at the US National Library of Medicine Medical Subject Headings (MeSH)
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.
PDGF/VEGF domain Provide feedback
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External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR000072Platelet-derived growth factor (PDGF) [PUBMED:2546599, PUBMED:1425569] is a potent mitogen for cells of mesenchymal origin, including smooth muscle cells and glial cells. In both mouse and human, the PDGF signalling network consists of four ligands, PDGFA-D, and two receptors, PDGFRalpha and PDGFRbeta. All PDGFs function as secreted, disulphide-linked homodimers, but only PDGFA and B can form functional heterodimers. PDGFRs also function as homo- and heterodimers. All known PDGFs have characteristic `PDGF domains', which include eight conserved cysteines that are involved in inter- and intramolecular bonds. Alternate splicing of the A chain transcript can give rise to two different forms that differ only in their C-terminal extremity. The transforming protein of Woolly monkey sarcoma virus (WMSV) (Simian sarcoma virus), encoded by the v-sis oncogene, is derived from the B chain of PDGF.
PDGFs are mitogenic during early developmental stages, driving the proliferation of undifferentiated mesenchyme and some progenitor populations. During later maturation stages, PDGF signalling has been implicated in tissue remodelling and cellular differentiation, and in inductive events involved in patterning and morphogenesis. In addition to driving mesenchymal proliferation, PDGFs have been shown to direct the migration, differentiation and function of a variety of specialised mesenchymal and migratory cell types, both during development and in the adult animal [PUBMED:12952899]. Other growth factors in this family include vascular endothelial growth factors B and C (VEGF-B, VEGF-C) [PUBMED:8637916, PUBMED:8617204] which are active in angiogenesis and endothelial cell growth, and placenta growth factor (PlGF) which is also active in angiogenesis [PUBMED:7681160].
PDGF is structurally related to a number of other growth factors which also form disulphide-linked homo- or heterodimers.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||membrane (GO:0016020)|
|Molecular function||growth factor activity (GO:0008083)|
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:
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This example describes an architecture with one
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EGFdomains, and finally a single
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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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The cytokine families in this clan have the cystine-knot fold. In this 6 cysteines form three disulphide bridges that are interlinked.
The clan contains the following 11 members:Coagulin Cys_knot DAN Hormone_6 IL17 NGF Noggin PDGF Sclerostin Spaetzle TGF_beta
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:
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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.
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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.
|Author:||Finn RD, Bateman A|
|Number in seed:||32|
|Number in full:||796|
|Average length of the domain:||81.90 aa|
|Average identity of full alignment:||34 %|
|Average coverage of the sequence by the domain:||29.98 %|
|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.
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There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.
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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.
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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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There are 5 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 PDGF domain has been found. There are 115 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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