Summary: Fibrinogen alpha C domain
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Fibrinogen Edit Wikipedia article
|fibrinogen alpha chain|
|Locus||Chr. 4 q28|
|fibrinogen beta chain|
|Locus||Chr. 4 q28|
|Fibrinogen gamma chain|
|Locus||Chr. 4 q28|
|Fibrinogen alpha/beta chain family|
crystal structure of native chicken fibrinogen with two different bound ligands
|Fibrinogen alpha C domain|
|Fibrinogen beta and gamma chains, C-terminal globular domain|
crystal structure of native chicken fibrinogen with two different bound ligands
Fibrinogen (factor I) is a glycoprotein that in vertebrates circulates in the blood. During tissue and vascular injury it is converted enzymatically by thrombin to fibrin and subsequently to a fibrin-based blood clot. Fibrinogen functions primarily to occlude blood vessels and thereby stop excessive bleeding. However, fibrinogen's product, fibrin, binds and reduces the activity of thrombin. This activity, sometimes referred to as antithrombin I, serves to limit blood clotting. Loss or reduction in this antithrombin 1 activity due to mutations in fibrinogen genes or hypo-fibrinogen conditions can lead to excessive blood clotting and thrombosis. Fibrin also mediates blood platelet and endothelial cell spreading, tissue fibroblast proliferation, capillary tube formation, and angiogenesis and thereby functions to promote tissue revascularization, wound healing, and tissue repair.
Reduced and/or dysfunctional fibrinogens occur in various congenital and acquired human fibrinogen-related disorders. These disorders represent a clinically important group of rare conditions in which individuals may present with severe episodes of pathological bleeding and thrombosis; these conditions are treated by supplementing blood fibrinogen levels and inhibiting blood clotting, respectively. Certain of these disorders may also be the cause of liver and kidney diseases.
Fibrinogen is a "positive" acute-phase protein, i.e. its blood levels rise in response to systemic inflammation, tissue injury, and certain other events. It is also elevated in various cancers. Elevated levels of fibrinogen in inflammation as well as cancer and other conditions have been suggested to be the cause of thrombosis and vascular injury that accompanies these conditions.
- 1 Genes
- 2 Structure
- 3 Blood clot formation
- 4 Fibrinogen disorders
- 5 Laboratory Tests
- 6 Hyperfibrinogenemia
- 7 References
- 8 External links
Fibrinogen is made and secreted into the blood primarily by liver hepatocyte cells. Endothelium cells are also reported to make what appears to be small amounts of fibrinogen but this fibrinogen has not been fully characterized; blood platelets and their precursors, bone marrow megakaryocytes, while once thought to make fibrinogen, are now known to take up and store but not make the glycoprotein. The final secreted, hepatocyte-derived glycoprotein is composed of two trimers with each trimer composed of three different polypeptide chains, the fibrinogen alpha chain (also termed the Aα or α chain) encoded by the FGA gene, the fibrinogen beta chain (also termed the Bβ or β chain) encoded by the FGB gene, and the fibrinogen gamma chain (also termed the γ chain) encoded by the FGG gene. All three genes are located on the long or "p" arm of human chromosome 4 (at positions 4q31.3, 4q31.3, and 4q32.1, respectively). Alternate splicing of the FGA gene produces a minor expanded isoform of Aα termed AαE which replaces Aα in 1–3% of circulating fibrinogen; alternate splicing of FGG produces a minor isoform of γ termed γ' which replaces γ in 8–10% of circulating fibrinogen; FGA is not alternatively spliced. Hence, the final fibrinogen product is composed principally of Aα, Bβ, and γ chains with a small percentage of it containing AαE and/or γ' chains in place of Aα and/or γ chains, respectively. The three genes are transcribed and translated in co-ordination by a mechanism(s) which remains incompletely understood. The coordinated transcription of these three fibrinogen genes is rapidly and greatly increased by systemic conditions such as inflammation and tissue injury. Cytokines produced during these systemic conditions, such as interleukin 6 and interleukin 1β, appear responsible for up-regulating this transcription.
The Aα, Bβ, and γ chains are transcribed and translated coordinately on the endoplasmic reticulum (ER) with their peptide chains being passed into the ER while their signal peptide portions are removed. Inside the ER, the three chains are assembled initially into Aαγ and Bβγ dimers, then to AαBβγ trimers, and finally to (AαBβγ)2 heximers, i.e. two AαBβγ trimers joined together by numerous disulfide bonds. The heximer is transferred to the Golgi where it is glycosylated, hydroxylated, sulfated, and phosphorylated to form the mature fibrinogen glycoprotein that is secreted into the blood. Mature fibrinogen is arranged as a long flexible protein array of three nodules held together by a very thin thread which is estimated to have a diameter between 8 and 15 Angstrom (Å). The two end nodules (termed D regions or domains) are alike in consisting of Bβ and γ chains while the center slightly smaller nodule (termed the E region or domain) consists of two intertwined Aα alpha chains. Measurements of shadow lengths indicate that nodule diameters are in the range 50 to 70 Å. The length of the dried molecule is 475 ± 25 Å.
The fibrinogen molecule circulates as a soluble plasma glycoprotein with a typical molecular weight (depending on its content of Aα verses AαE and γ versus γ' chains) of ~340 kDa. It has a rod-like shape with dimensions of 9 × 47.5 × 6 nm and has a negative net charge at physiological pH ( its isoelectric point is pH 5.8). The normal concentration of fibrinogen in blood plasma is 150–400 mg/dL with levels appreciably below or above this range associated with pathological bleeding and/or thrombosis. Fibrinogen has a circulating half-life of ~4 days.
Blood clot formation
During blood clotting, thrombin attacks the N-terminus of the Aα and Bβ chains in fibrinogen to form individual fibrin strands plus two small polypeptides, fibrinopeptides a and b derived from these respective chains. The individual fibrin strands then polymerize and are cross-linked with other fibrin stands by blood factor XIIIa to form an extensive interconnected fibrin network that is the basis for the formation of a mature fibrin clot. In addition to forming fibrin, fibrinogen also promotes blood clotting by forming bridges between, and activating, blood platelets through binding to their GpIIb/IIIa surface membrane fibrinogen receptor.
Fibrin participates in limiting blood clot formation and lysing formed blood clots by at least two important mechanisms. First, it possesses three low affinity binding sites (two in fibrin's E domain; one in its D domain) for thrombin; this binding sequesters thrombin from attacking fibrinogen. Second, fibrin's Aα chain accelerates by at least 100-fold the mount of plasmin activated by tissue plasminogen activator; plasmin breaks-down blood clots. Plasmin's attack on fibrin releases D-dimers (also termed DD dimers). The detection of these dimers in blood is used as a clinical test for fibrinolysis.
Several disorders in the quantity and/or quality of fibrinogen cause pathological bleeding, pathological blood clotting, and/or the deposition of fibrinogen in the liver, kidneys, and other tissues. The following list of these disorders briefly describes and compares them and gives linkages to main article Wikipedia pages that offer more complete descriptions.
Congenital afibrinogenemia is a rare and generally autosomal recessive inherited disorder in which blood does not clot due to a lack of fibrinogen (plasma fibrinogen levels typically 0 but sometimes detected at extremely low levels, e.g. <10 mg/dL. This severe disorder is usually caused by mutations in both the maternal and paternal copies of either the FGA, FGB, or FBG gene. The mutations have virtually complete genetic penetrance with essentially all homozygous bearers experiencing frequent and sometimes life-threatening episodes of bleeding and/or thrombosis. Pathological bleeding occurs early in life, for example often being seen at birth with excessive hemorrhage from the umbilicus.
Congenital hypofibrinogenemia is a rare inherited disorder in which blood may not clot normally due to reduced levels of fibrinogen (plasma fibrinogen typically <150 but >50 mg/dL). The disorder reflects a disruptive mutation in only one of the two parental FGA, FGB, or FBG genes and has a low degree of genetic penetrance, i.e. only some family members with the defective gene ever exhibit symptoms. Symptoms of the disorder, which more often occurs in individuals with lower plasma fibrinogen levels include episodic bleeding and thrombosis that typically begin in late childhood or adulthood.
Fibrinogen storage disease
Fibringogen storage disease is a extremely rare disorder. It is a form of congenital hypofibrinogenemia in which certain specific hereditary mutations in one copy of the FGG gene causes its fibrinogen product to accumulate in, and damage, liver cells. The disorder has not reported with FGA or FGB mutations. Symptoms of these FGG mutations have a low level of penetrance. The plasma fibrinogen levels (generally <150 but >50 mg/dL) detected in this disorder reflect the fibrinogen made by the normal gene. Fibrinogen storage disease may lead to abnormal bleeding and thrombosis but is distinguished by also sometimes leading to liver cirrhosis.
Congenital dysfibrinogenemia is a rare autosomal dominant inherited disorder in which plasma fibrinogen is composed of a dysfunctional fibrinogen made by a mutated FGA, FGB, or FBG gene inherited from one parent plus a normal fibrinogen made by a normal gene inherited from the other parent. As a reflection of this duality, plasma fibrinogen levels measured by immunological methods are normal (>150 mg/dL) but are c. 50% lower when measured by clot formation methods. The disorder exhibits reduced penetrance with only some individuals with the abnormal gene showing symptoms of abnormal bleeding and thrombosis.
Hereditary fibrinogen Aα-Chain amyloidosis
Hereditary fibrinogen Aα-Chain amyloidosis is an autosomal dominant extremely rare inherited disorder caused by a mutation in one of the two copies of the FGA gene. It is a form of congenital dysfibrinogenemia in which certain mutations lead to the production of an abnormal fibrinogen that circulates in the blood while gradually accumulating in the kidney. This accumulation leads over time to one form of familial renal amyloidosis. Plasma fibrinogen levels are similar to that seen in other forms of congenital dαysfibrinogenemia. Fibrinogen Aα-Chain amyloidosis has not associated with abnormal bleeding or thrombosis.
Acquired dysfibrinogenemia is a rare disorder in which circulating fibrinogen is composed at least in part of a dysfunctional fibrinogen due to various acquired diseases. One well-studied cause of the disorder is severe liver disease including hepatoma, chronic active hepatitis, cirrhosis, and jaundice due to biliary tract obstruction. The diseased liver synthesizes a fibrinogen which has a normally functional amino acid sequence but is incorrectly glycosylated (i.e. has a wrong amount of sugar residues) added to it during its passage through the Golgi. The incorrectly glycosalated fibrinogen is dysfunctional and may cause pathological episodes of bleeding and/or blood clotting. Other, less well understood, causes are plasma cell dyscrasias and autoimmune disorders in which a circulating abnormal immunoglobulin or other protein interferes with fibrinogen function, and rare cases of cancer and medication (isotretinoin, glucocorticoids, and antileukemic drugs) toxicities.
Congenital hypodysfibrinogenemia is a rare inherited disorder in which low levels (i.e. <150 mg/d) of immunologically detected plasma fibrinogen are and composed at least in part of a dysfunctional fibrinogen. The disorder reflects mutations typically in both inherited fibrinogen genes one of which produces a dysfunctional fibrinogen while the other produces low amounts of fibrinogen. The disorder, while having reduced penetrance is usually more severe that congenital dysfibrinogenemia but like the latter disorder causes pathological episodes of bleeding and/or blood clotting.
Cryofibrinogenemia is an acquired disorder in which fibrinogen precipitates at cold temperatures and may lead to the intravascular precipitation of fibrinogen, fibrin, and other circulating proteins thereby causing the infarction of various tissues and bodily extremities. Cryoglobulonemia may occur without evidence of an underlying associated disorders, i.e. primary cryoglobulinemia (also termed essential cryoglobulinemia) or, far more commonly, with evidence of an underlying disease, i.e. secondary cryoglobulonemia. Secondary cryofibrinoenemia can develop in individuals suffering infection (c. 12% of cases), malignant or premalignant disorders (21%), vasculitis (25%), and autoimmune diseases (42%). In these cases, cryofibinogenema may or may not cause tissue injury and/or other symptoms and the actual cause-effect relationship between these diseases and the development of cryofibrinogenmia is unclear. Cryofibrinogenemia can also occur in association with the intake of certain drugs.
Acquired hypofibrinogenemia is a deficiency in circulating fibrinogen due to excessive consumption that may occur as a result of trauma, certain phases of disseminated intravascular coagulation, and sepsis. It may also occur as a result of hemodilution as a result of blood losses and/or transfusions with packed red blood cells or other fibrinogen-poor whole blood replacements.
Clinical analyses of the fibrinogen disorders typically measure blood clotting using the following successive steps: Higher levels are, amongst others, associated with cardiovascular disease (>3.43 g/L). It may be elevated in any form of inflammation, as it is an acute-phase protein; for example, it is especially apparent in human gingival tissue during the initial phase of periodontal disease.
- Blood clotting is measured using standard tests, e.g. prothrombin time, partial thromboplastin time, thrombin time, and/or reptilase time; low fibrinogen levels and dysfunctional fibrinogens usually prolong these times whereas the lack of fibrinogen (i.e. afibrinogenemia) renders these times infinitely prolonged.
- Antigenic levels of fibrinogen levels are measured in the plasma isolated from venous blood by immunoassays with normal levels being about 1.5-3 gram/liter, depending on the method used. These levels are normal in dysfibrinogenmia (i.e. 1.5-3 gram/liter), decreased in hypofibrinogenemia and hypdysfibrinogenemia (i.e. <1.5 gram/liter), and absent (i.e. <0.02 gram/liter) in afibrinogenima.
- Functional levels of fibrinogen are measured on plasma induced to clot. The levels of clotted fibrinogen in this test should be decreased in hypofibrinogenemia, hypodysfibrinogenemia, and dysfibrinogenemia and undetectable in afibrinogenemia.
- Functional fibrinogen/antigenic fibrinogen levels are <0.7 in hypofibrinogenemia, hypodsyfibrinogenemia, and dysfibringognemia and not applicable in afibringenemia.
- Fibrinogen analysis can also be tested on whole-blood samples by thromboelastometry. This analysis investigates the interaction of coagulation factors, their inhibitors, anticoagulant drugs, blood cells, specifically platelets, during clotting and subsequent fibrinolysis as it occurs in whole blood. The test provides information on hemostatic efficacy and maximum clod firmness to give additional information on fibrin-platelet interactions and the rate of fibrinolysis (see Thromboelastometry).
- Scanning electron microscopy and confocal laser scanning microscopy of in vitro-formed clots can give information on fibrin clot density and architecture.
- The fibrinogen uptake test or fibrinogen scan was formerly used to detect deep vein thrombosis. In this method, radioactively labeled fibrinogen, typically with radioiodine, is given to individuals, incorporated into a thrombus, and detected by scintigraphy.
Levels of functionally normal fibrinogen increase in pregnancy to an average of 4.5 gram/liter compared to an average of 3 g/l in non-pregnant people. They may also increase in various forms of cancer, particularly gastric, lung, prostate, and ovarian cancers. In these cases, the hyperfibrinogenemia may contribute to the development of pathological thrombosis. A particular pattern of migratory superficial vein thrombosis, termed trousseau's syndrome, occurs in, and may precede all other signs and symptoms of, these cancers. Hyperfibrinogenmia has also been linked as a cause of persistent pulmonary hypertension of the newborn and post-operative thrombosis. High fibrinogen levels had been proposed as a predictor of hemorrhagic complications during catheter-directed trombolysis for acute or subacute peripheral native artery and arterial bypass occlusions. However, a systematic review of the available literature until January 2016 found that the predictive value of plasma fibrinogen level for predicting hemorrhagic complications after catheter-directed thrombolysis is unproven.
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|Wikimedia Commons has media related to Fibrinogen.|
- Jennifer McDowall/Interpro: Protein of the Month: Fibrinogen.
- D'Eustachio/reactome: fibrinogen → fibrin monomer + 2 fibrinopeptide A + 2 fibrinopeptide B
- Khan Academy Medicine (on YouTube): Clotting 1 - How do we make blood clots?
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.
Fibrinogen alpha C domain Provide feedback
This domain family is found in eukaryotes, and is approximately 70 amino acids in length, and the family is found in association with PF08702. This domain is the C terminal domain of fibrinogen in mammals. The domain lies in the C terminal half of the alpha C region in these proteins. The function of the domain is that of intramolecular and intermolecular interactions to form fibrin.
Burton RA, Tsurupa G, Hantgan RR, Tjandra N, Medved L;, Biochemistry. 2007;46:8550-8560.: NMR solution structure, stability, and interaction of the recombinant bovine fibrinogen alphaC-domain fragment. PUBMED:17590019 EPMC:17590019
This tab holds annotation information from the InterPro database.
InterPro entry IPR021996
This domain family is found in eukaryotes, and is approximately 70 amino acids in length, and the family is found in association with INTERPRO. This domain is the C-terminal domain of fibrinogen in mammals. The domain lies in the C-terminal half of the alpha C region in these proteins. The function of the domain is that of intramolecular and intermolecular interactions to form fibrin.
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- an HTML-based representation of the alignment, coloured according to the posterior-probability (PP) values from the HMM. As for the standard HTML view, heatmap alignments can also be very large and slow to render.
You can download (or view in your browser) a text representation of a Pfam alignment in various formats:
You can also change the order in which sequences are listed in the alignment, change how insertions are represented, alter the characters that are used to represent gaps in sequences and, finally, choose whether to download the alignment or to view it in your browser directly.
You may find that large alignments cause problems for the viewers and the reformatting tool, so we also provide all alignments in Stockholm format. You can download either the plain text alignment, or a gzipped version of it.
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...
If you find these logos useful in your own work, please consider citing the following article:
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:||Mistry J , Gavin OL|
|Number in seed:||13|
|Number in full:||71|
|Average length of the domain:||68.00 aa|
|Average identity of full alignment:||47 %|
|Average coverage of the sequence by the domain:||8.25 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 45638612 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||8|
|Download:||download the raw HMM for this family|
Weight segments by...
Change the size of the sunburst
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a FASTA-format file
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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:
- show/hide the summary boxes
- highlight species that are represented in the seed alignment
- expand/collapse the tree or expand it to a given depth
- select a sub-tree or a set of species within the tree and view them graphically or as an alignment
- save a plain text representation of the tree
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.
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 Fibrinogen_aC domain has been found. There are 2 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 sequence.
Loading structure mapping...