Summary: Indoleamine 2,3-dioxygenase
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Indoleamine 2,3-dioxygenase Edit Wikipedia article
|, IDO, IDO-1, INDO, indoleamine 2,3-dioxygenase 1|
Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO EC 18.104.22.168) is a heme-containing enzyme that in humans is encoded by the IDO1 gene. It is one of three enzymes that catalyze the first and rate-limiting step in the kynurenine pathway, the O2-dependent oxidation of L-tryptophan to N-formylkynurenine, the others being IDO2  and tryptophan 2,3-dioxygenase (TDO).
IDO has been implicated in immune modulation through its ability to limit T cell function and engage mechanisms of immune tolerance. Emerging evidence suggests that IDO becomes activated during tumor development, helping malignant cells escape eradication by the immune system.
Indoleamine 2,3-dioxygenase is the first and rate-limiting enzyme of tryptophan catabolism through the kynurenine pathway, thus causing depletion of tryptophan which can cause halted growth of microbes as well as T cells. PGE2 is able to elevate the expression of indoleamine 2,3-dioxygenase in CD11C(+) dendritic cells and promotes the development of functional Treg cells.
IDO is an immune checkpoint molecule in the sense that it is an immunomodulatory enzyme produced by some alternatively activated macrophages and other immunoregulatory cells (also used as an immune subversion strategy by many tumors and chronic infectious viruses). IDO is known to suppress T and NK cells, generate and activate Tregs and myeloid-derived suppressor cells, and promote tumour angiogenesis.
Interferon-gamma has an antiproliferative effect on many tumor cells and inhibits intracellular pathogens such as Toxoplasma and Chlamydia, at least partly because of the induction of indoleamine 2,3-dioxygenase.
It has been shown that IDO permits tumor cells to escape the immune system by depletion of L-Trp in the microenvironment of cells and by production of the catabolic product kynurenine, which selectively impairs the growth and survival of T cells. A wide range of human cancers such as prostatic, colorectal, pancreatic, cervical, gastric, ovarian, head, lung, etc. overexpress human IDO (hIDO).
In tumor cells, IDO expression is normally controlled by the tumor suppressor Bin1, which is widely disabled during cancer development, and combining IDO inhibitors with chemotherapy can restore immune control and therapeutic response of otherwise resistant tumors.
Norharmane, via inhibition of indoleamine 2,3-dioxygenase exerts neuroprotective properties by suppressing kynurenine neurotoxic metabolites such as quinolinic acid, 3-hydroxy-kynurenine and nitric oxide synthase.
1-Methyltryptophan is a racemic compound that weakly inhibits indoleamine dioxygenase, but is also a very slow substrate. The specific racemer 1-methyl-D-tryptophan (known as indoximod) is in clinical trials for various cancers.
Epacadostat (INCB24360) and navoximod (GDC-0919) are potent inhibitors of the indoleamine 2,3-dioxygenase enzyme and are in clinical trials for various cancers. BMS-986205 is also in clinical trials for cancer.
crystal structure of 4-phenylimidazole bound form of human indoleamine 2,3-dioxygenase
|PDB structures||RCSB PDB PDBe PDBsum|
|Gene Ontology||AmiGO / QuickGO|
It was originally thought that the mechanism of tryptophan oxidation occurred by base-catalysed abstraction, but it is now thought that the mechanism involves formation of a transient ferryl (i.e. high-valent iron) species.
There are crystal structures for human IDO in complex with the inhibitor 4-phenylimidazole and other inhibitors. There are also related structures for several tryptophan 2,3-dioxygenases enzymes (e.g. for X. campestris and human TDO - see tryptophan 2,3-dioxygenase).
- GRCh38: Ensembl release 89: ENSG00000131203 - Ensembl, May 2017
- GRCm38: Ensembl release 89: ENSMUSG00000031551 - Ensembl, May 2017
- "Human PubMed Reference:".
- "Mouse PubMed Reference:".
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- Targeting the indoleamine 2,3-dioxygenase pathway in cancer 2013
-  Another Immune Checkpoint Emerges as Anticancer Target 2013
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- Abdollahi, Mostafa: Case Study Oshtoran Syndrome  Retrieved June 3, 2016
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- IDO Plus PD-1 Inhibitor Combo Sparks Responses in Bladder and Cervical Cancers
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- Yanagisawa S, Yotsuya K, Hashiwaki Y, Horitani M, Sugimoto H, Shiro Y, Appelman EH, Ogura T. "Identification of the Fe-O2 and the Fe=O heme species for indoleamine 2,3-dioxygenase during catalytic turnover". Chem Lett. 39: 36–37. doi:10.1246/cl.2010.36.
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- Sugimoto H, Oda S, Otsuki T, Hino T, Yoshida T, Shiro Y (February 2006). "Crystal structure of human indoleamine 2,3-dioxygenase: catalytic mechanism of O2 incorporation by a heme-containing dioxygenase" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 103 (8): 2611–6. doi:10.1073/pnas.0508996103. PMID 16477023.
- Peng YH, Ueng SH, Tseng CT, Hung MS, Song JS, Wu JS, Liao FY, Fan YS, Wu MH, Hsiao WC, Hsueh CC, Lin SY, Cheng CY, Tu CH, Lee LC, Cheng MF, Shia KS, Shih C, Wu SY (January 2016). "Important Hydrogen Bond Networks in Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitor Design Revealed by Crystal Structures of Imidazoleisoindole Derivatives with IDO1". Journal of Medicinal Chemistry. 59 (1): 282–93. doi:10.1021/acs.jmedchem.5b01390. PMID 26642377.
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- Takikawa O (December 2005). "Biochemical and medical aspects of the indoleamine 2,3-dioxygenase-initiated L-tryptophan metabolism". Biochemical and Biophysical Research Communications. 338 (1): 12–9. doi:10.1016/j.bbrc.2005.09.032. PMID 16176799.
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- Kobayashi K, Hayashi K, Sono M (September 1989). "Effects of tryptophan and pH on the kinetics of superoxide radical binding to indoleamine 2,3-dioxygenase studied by pulse radiolysis". The Journal of Biological Chemistry. 264 (26): 15280–3. PMID 2549057.
- Daley-Yates PT, Powell AP, Smith LL (November 1988). "Pulmonary indoleamine 2,3-dioxygenase activity and its significance in the response of rats, mice, and rabbits to oxidative stress". Toxicology and Applied Pharmacology. 96 (2): 222–32. doi:10.1016/0041-008X(88)90082-8. PMID 2848333.
- Burkin DJ, Kimbro KS, Barr BL, Jones C, Taylor MW, Gupta SL (July 1993). "Localization of the human indoleamine 2,3-dioxygenase (IDO) gene to the pericentromeric region of human chromosome 8". Genomics. 17 (1): 262–3. doi:10.1006/geno.1993.1319. PMID 8406467.
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Indoleamine 2,3-dioxygenase Provide feedback
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|Similarity to PfamA using HHSearch:||DUF1864|
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR000898
Indoleamine 2,3-dioxgyenase (IDO, EC) [PUBMED:1907934] is a cytosolic haem protein which, together with the hepatic enzyme tryptophan 2,3-dioxygenase, catalyzes the conversion of tryptophan and other indole derivatives to kynurenines. The physiological role of IDO is not fully understood but is of great interest, because IDO is widely distributed in human tissues, can be up-regulated via cytokines such as interferon-gamma, and can thereby modulate the levels of tryptophan, which is vital for cell growth. The degradative action of IDO on tryptophan leads to cell death by starvation of this essential and relatively scarce amino acid. IDO is a haem-containing enzyme of about 400 amino acids. Site-directed mutagenesis showed His346 (SWISSPROT) to be essential for haem binding, indicating that this histidine residue may be the proximal ligand. Mutation of Asp274 also compromised the ability of IDO to bind haem, suggesting that Asp274 may coordinate to haem directly as the distal ligand or is essential in maintaining the conformation of the haem pocket [PUBMED:12766158].
Other proteins that are evolutionarily related to IDO include yeast hypothetical protein YJR078w; and myoglobin from the red muscle of the archaeogastropodic molluscs, Nordotis madaka (Giant abalone) and Sulculus diversicolor [PUBMED:8011076, PUBMED:12711393]. These unusual globins lack enzymatic activity but have kept the haem group.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||heme binding (GO:0020037)|
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|Author:||Finn RD, Bateman A|
|Number in seed:||189|
|Number in full:||1502|
|Average length of the domain:||359.90 aa|
|Average identity of full alignment:||26 %|
|Average coverage of the sequence by the domain:||70.41 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 26740544 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||17|
|Download:||download the raw HMM for this family|
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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.
There is 1 interaction 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 IDO domain has been found. There are 20 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...