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10  structures 907  species 1  interaction 2269  sequences 58  architectures

Family: A_deamin (PF02137)

Summary: Adenosine-deaminase (editase) domain

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This is the Wikipedia entry entitled "Adenosine deaminase". More...

Adenosine deaminase Edit Wikipedia article

Adenosine deaminase 1VFL.png
Available structures
PDB Ortholog search: PDBe RCSB
Aliases ADA, entrez:100, Adenosine deaminase
External IDs OMIM: 608958 MGI: 87916 HomoloGene: 37249 GeneCards: ADA
Gene location (Human)
Chromosome 20 (human)
Chr. Chromosome 20 (human)[1]
Chromosome 20 (human)
Genomic location for ADA
Genomic location for ADA
Band 20q13.12 Start 44,619,522 bp[1]
End 44,652,233 bp[1]
RNA expression pattern
PBB GE ADA 216705 s at fs.png

PBB GE ADA 204639 at fs.png
More reference expression data
Species Human Mouse
RefSeq (mRNA)



RefSeq (protein)



Location (UCSC) Chr 20: 44.62 – 44.65 Mb Chr 2: 163.73 – 163.75 Mb
PubMed search [3] [4]
View/Edit Human View/Edit Mouse
Adenosine/AMP deaminase
PDB 2amx EBI.jpg
crystal structure of plasmodium yoelii adenosine deaminase (py02076)
Symbol A_deaminase
Pfam PF00962
Pfam clan CL0034
InterPro IPR001365
SCOP 1add
CDD cd01320
Adenosine deaminase (editase) domain
Symbol A_deamin
Pfam PF02137
InterPro IPR002466
SCOP 1add
Adenosine/AMP deaminase N-terminal
Symbol A_deaminase_N
Pfam PF08451
InterPro IPR013659

Adenosine deaminase (also known as adenosine aminohydrolase, or ADA) is an enzyme (EC involved in purine metabolism. It is needed for the breakdown of adenosine from food and for the turnover of nucleic acids in tissues.

Its primary function in humans is the development and maintenance of the immune system.[5] However, the full physiological role of ADA is not yet completely understood.[6]


ADA exists in both small form (as a monomer) and large form (as a dimer-complex).[6] In the monomer form, the enzyme is a polypeptide chain,[7] folded into eight strands of parallel α/β barrels, which surround a central deep pocket that is the active site.[5] In addition to the eight central β-barrels and eight peripheral α-helices, ADA also contains five additional helices: residues 19-76 fold into three helices, located between β1 and α1 folds; and two antiparallel carboxy-terminal helices are located across the amino-terminal of the β-barrel.

The ADA active site contains a zinc ion, which is located in the deepest recess of the active site and coordinated by five atoms from His15, His17, His214, Asp295, and the substrate.[5] Zinc is the only cofactor necessary for activity.

The substrate, adenosine, is stabilized and bound to the active site by nine hydrogen bonds.[5] The carboxyl group of Glu217, roughly coplanar with the substrate purine ring, is in position to form a hydrogen bond with N1 of the substrate. The carboxyl group of Asp296, also coplanar with the substrate purine ring, forms hydrogen bond with N7 of the substrate. The NH group of Gly184 is in position to form a hydrogen bond with N3 of the substrate. Asp296 forms bonds both with the Zn2+ ion as well as with 6-OH of the substrate. His238 also hydrogen bonds to substrate 6-OH. The 3'-OH of the substrate ribose forms a hydrogen bond with Asp19, while the 5'-OH forms a hydrogen bond with His17. Two further hydrogen bonds are formed to water molecules, at the opening of the active site, by the 2'-OH and 3'-OH of the substrate.

Due to the recessing of the active site inside the enzyme, the substrate, once bound, is almost completely sequestered from solvent.[5] The surface exposure of the substrate to solvent when bound is 0.5% the surface exposure of the substrate in the free state.


ADA irreversibly deaminates adenosine, converting it to the related nucleoside inosine by the substitution of the amino group for a keto group.


Inosine can then be deribosylated (removed from ribose) by another enzyme called purine nucleoside phosphorylase (PNP), converting it to hypoxanthine.

Mechanism of catalysis

The proposed mechanism for ADA-catalyzed deamination is stereospecific addition-elimination via tetrahedral intermediate.[8] By either mechanism, Zn2+ as a strong electrophile activates a water molecule, which is deprotonated by the basic Asp295 to form the attacking hydroxide.[5] His238 orients the water molecule and stabilizes the charge of the attacking hydroxide. Glu217 is protonated to donate a proton to N1 of the substrate.

The reaction is stereospecific due to the location of the zinc, Asp295, and His238 residues, which all face the B-side of the purine ring of the substrate.[5]

Competitive inhibition has been observed for ADA, where the product inosine acts at the competitive inhibitor to enzymatic activity.[9]


ADA is considered one of the key enzymes of purine metabolism.[8] The enzyme has been found in bacteria, plants, invertebrates, vertebrates, and mammals, with high conservation of amino acid sequence.[6] The high degree of amino acid sequence conservation suggests the crucial nature of ADA in the purine salvage pathway.

Primarily, ADA in humans is involved in the development and maintenance of the immune system. However, ADA association has also been observed with epithelial cell differentiation, neurotransmission, and gestation maintenance.[10] It has also been proposed that ADA, in addition to adenosine breakdown, stimulates release of excitatory amino acids and is necessary to the coupling of A1 adenosine receptors and heterotrimeric G proteins.[6] Adenosine deaminase deficiency leads to pulmonary fibrosis,[11] suggesting that chronic exposure to high levels of adenosine can exacerbate inflammation responses rather than suppressing them. It has also been recognized that adenosine deaminase protein and activity is upregulated in mouse hearts that overexpress HIF-1 alpha, which in part explains the attenuated levels of adenosine in HIF-1 alpha expressing hearts during ischemic stress.[12]


Some mutations in the gene for adenosine deaminase cause it not to be expressed. The resulting deficiency is one cause of severe combined immunodeficiency (SCID), particularly of autosomal recessive inheritance.[13] Deficient levels of ADA have also been associated with pulmonary inflammation, thymic cell death, and defective T-cell receptor signaling.[14][15]

Conversely, mutations causing this enzyme to be overexpressed are one cause of hemolytic anemia .[16]

There is some evidence that a different allele (ADA2) may lead to autism.[17]

Elevated levels of ADA has also been associated with AIDS.[14][18]


There are 2 isoforms of ADA: ADA1 and ADA2.

  • ADA1 is found in most body cells, particularly lymphocytes and macrophages, where it is present not only in the cytosol and nucleus but also as the ecto- form on the cell membrane attached to dipeptidyl peptidase-4 (aka, CD26). ADA1 is involved mostly in intracellular activity, and exists both in small form (monomer) and large form (dimer).[6] The interconversion of small to large forms is regulated by a 'conversion factor' in the lung.[19]
  • ADA2 was first identified in human spleen.[20] It was subsequently found in other tissues including the macrophage where it co-exists with ADA1. The two isoforms regulate the ratio of adenosine to deoxyadenosine potentiating the killing of parasites. ADA2 is found predominantly in the human plasma and serum, and exists solely as a homodimer.[21]

Clinical significance

ADA2 is the predominant form present in human blood plasma and is increased in many diseases, particularly those associated with the immune system: for example rheumatoid arthritis, psoriasis, and sarcoidosis. The plasma ADA2 isoform is also increased in most cancers. ADA2 is not ubiquitous but co-exists with ADA1 only in monocytes-macrophages.[citation needed]

Total plasma ADA can be measured using high performance liquid chromatography or enzymatic or colorimetric techniques. Perhaps the simplest system is the measurement of the ammonia released from adenosine when broken down to inosine. After incubation of plasma with a buffered solution of adenosine the ammonia is reacted with a Berthelot reagent to form a blue colour which is proportionate to the amount of enzyme activity. To measure ADA2, erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) is added prior to incubation so as to inhibit the enzymatic activity of ADA1.[20] It is the absence of ADA1 that causes SCID.

ADA can also be used in the workup of lymphocytic pleural effusions or peritoneal ascites, in that such specimens with low ADA levels essentially excludes tuberculosis from consideration.[22]

Tuberculosis pleural effusions can now be diagnosed accurately by increased levels of pleural fluid adenosine deaminase, above 40 U per liter.[23]

Cladribine is an anti-neoplastic agent used in the treatment of hairy cell leukemia; its mechanism of action is inhibition of adenosine deaminase.

Coformycin was also described as a adenosine deaminase inhibitor but is alleged to be an antibiotic.

See also


  1. ^ a b c GRCh38: Ensembl release 89: ENSG00000196839 - Ensembl, May 2017
  2. ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000017697 - Ensembl, May 2017
  3. ^ "Human PubMed Reference:". 
  4. ^ "Mouse PubMed Reference:". 
  5. ^ a b c d e f g Wilson DK, Rudolph FB, Quiocho FA (May 1991). "Atomic structure of adenosine deaminase complexed with a transition-state analog: understanding catalysis and immunodeficiency mutations". Science. 252 (5010): 1278–1284. doi:10.1126/science.1925539. PMID 1925539. 
  6. ^ a b c d e Cristalli G, Costanzi S, Lambertucci C, Lupidi G, Vittori S, Volpini R, Camaioni E (Mar 2001). "Adenosine deaminase: functional implications and different classes of inhibitors". Medicinal Research Reviews. 21 (2): 105–128. doi:10.1002/1098-1128(200103)21:2<105::AID-MED1002>3.0.CO;2-U. PMID 11223861. 
  7. ^ Daddona PE, Kelley WN (Jan 1977). "Human adenosine deaminase. Purification and subunit structure". The Journal of Biological Chemistry. 252 (1): 110–115. PMID 13062. 
  8. ^ a b Losey HC, Ruthenburg AJ, Verdine GL (Jan 2006). "Crystal structure of Staphylococcus aureus tRNA adenosine deaminase TadA in complex with RNA". Nature Structural & Molecular Biology volume. 13 (2): 153–159. doi:10.1038/nsmb1047. 
  9. ^ Saboury AA, Divsalar A, Jafari GA, Moosavi-Movahedi AA, Housaindokht MR, Hakimelahi GH (May 2002). "A product inhibition study on adenosine deaminase by spectroscopy and calorimetry". Journal of Biochemistry and Molecular Biology. 35 (3): 302–305. doi:10.5483/BMBRep.2002.35.3.302. PMID 12297022. 
  10. ^ Moriwaki Y, Yamamoto T, Higashino K (Oct 1999). "Enzymes involved in purine metabolism--a review of histochemical localization and functional implications". Histology and Histopathology. 14 (4): 1321–1340. PMID 10506947. 
  11. ^ Blackburn MR (2003). "Too much of a good thing: adenosine overload in adenosine-deaminase-deficient mice". Trends in Pharmacological Sciences. 24 (2): 66–70. doi:10.1016/S0165-6147(02)00045-7. PMID 12559769. 
  12. ^ Wu J, Bond C, Chen P, Chen M, Li Y, Shohet RV, Wright G (2015). "HIF-1α in the heart: remodeling nucleotide metabolism". Journal of Molecular and Cellular Cardiology. 82: 194–200. doi:10.1016/j.yjmcc.2015.01.014. PMC 4405794Freely accessible. PMID 25681585. 
  13. ^ Sanchez JJ, Monaghan G, Børsting C, Norbury G, Morling N, Gaspar HB (May 2007). "Carrier frequency of a nonsense mutation in the adenosine deaminase (ADA) gene implies a high incidence of ADA-deficient severe combined immunodeficiency (SCID) in Somalia and a single, common haplotype indicates common ancestry". Annals of Human Genetics. 71 (Pt 3): 336–47. doi:10.1111/j.1469-1809.2006.00338.x. PMID 17181544. 
  14. ^ a b Blackburn MR, Kellems RE (2005). "Adenosine deaminase deficiency: metabolic basis of immune deficiency and pulmonary inflammation". Advances in Immunology. Advances in Immunology. 86: 1–41. doi:10.1016/S0065-2776(04)86001-2. ISBN 9780120044863. PMID 15705418. 
  15. ^ Apasov SG, Blackburn MR, Kellems RE, Smith PT, Sitkovsky MV (Jul 2001). "Adenosine deaminase deficiency increases thymic apoptosis and causes defective T cell receptor signaling". The Journal of Clinical Investigation. 108 (1): 131–141. doi:10.1172/JCI10360. PMC 209335Freely accessible. PMID 11435465. 
  16. ^ Chottiner EG, Cloft HJ, Tartaglia AP, Mitchell BS (Mar 1987). "Elevated adenosine deaminase activity and hereditary hemolytic anemia. Evidence for abnormal translational control of protein synthesis". The Journal of Clinical Investigation. 79 (3): 1001–5. doi:10.1172/JCI112866. PMC 424261Freely accessible. PMID 3029177. 
  17. ^ Persico AM, Militerni R, Bravaccio C, Schneider C, Melmed R, Trillo S, Montecchi F, Palermo MT, Pascucci T, Puglisi-Allegra S, Reichelt KL, Conciatori M, Baldi A, Keller F (Dec 2000). "Adenosine deaminase alleles and autistic disorder: case-control and family-based association studies". American Journal of Medical Genetics. 96 (6): 784–90. doi:10.1002/1096-8628(20001204)96:6<784::AID-AJMG18>3.0.CO;2-7. PMID 11121182. 
  18. ^ Cowan MJ, Brady RO, Widder KJ (Feb 1986). "Elevated erythrocyte adenosine deaminase activity in patients with acquired immunodeficiency syndrome". Proceedings of the National Academy of Sciences of the United States of America. 83 (4): 1089–1091. doi:10.1073/pnas.83.4.1089. PMC 323016Freely accessible. PMID 3006027. 
  19. ^ Schrader WP, Stacy AR (Sep 1977). "Purification and subunit structure of adenosine deaminase from human kidney". The Journal of Biological Chemistry. 252 (18): 6409–6415. PMID 893413. 
  20. ^ a b Schrader WP, Pollara B, Meuwissen HJ (Jan 1978). "Characterization of the residual adenosine deaminating activity in the spleen of a patient with combined immunodeficiency disease and adenosine deaminase deficiency". Proceedings of the National Academy of Sciences of the United States of America. 75 (1): 446–50. doi:10.1073/pnas.75.1.446. PMC 411266Freely accessible. PMID 24216. 
  21. ^ Zavialov AV, Engström A (Oct 2005). "Human ADA2 belongs to a new family of growth factors with adenosine deaminase activity". The Biochemical Journal. 391 (Pt 1): 51–57. doi:10.1042/BJ20050683. PMC 1237138Freely accessible. PMID 15926889. 
  22. ^ Jiménez Castro D, Díaz Nuevo G, Pérez-Rodríguez E, Light RW (2003). "Diagnostic value of adenosine deaminase in nontuberculous lymphocytic pleural effusions" (PDF). Eur. Respir. J. 21 (2): 220–4. doi:10.1183/09031936.03.00051603. PMID 12608433. 
  23. ^ Brunicardi F, Andersen D, Billiar T, Dunn D, Hunter J, Pollock RE (2005). "Chapter 18, question 16". Schwartz's principles of surgery (8th ed.). New York: McGraw-Hill Professional. ISBN 978-0071410908. 

Further reading

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This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

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.

Adenosine-deaminase (editase) domain Provide feedback

Adenosine deaminases acting on RNA (ADARs) can deaminate adenosine to form inosine. In long double-stranded RNA, this process is non-specific; it occurs site-specifically in RNA transcripts. The former is important in defence against viruses, whereas the latter may affect splicing or untranslated regions. They are primarily nuclear proteins, but a longer isoform of ADAR1 is found predominantly in the cytoplasm. ADARs are derived from the Tad1-like tRNA deaminases that are present across eukaryotes. These in turn belong to the nucleotide/nucleic acid deaminase superfamily and are characterized by a distinct insert between the two conserved cysteines that are involved in binding zinc [2].

Literature references

  1. Keegan LP, Leroy A, Sproul D, O'Connell MA; , Genome Biol 2004;5:209.: Adenosine deaminases acting on RNA (ADARs): RNA-editing enzymes. PUBMED:14759252 EPMC:14759252

  2. Iyer LM, Zhang D, Rogozin IB, Aravind L;, Nucleic Acids Res. 2011; [Epub ahead of print]: Evolution of the deaminase fold and multiple origins of eukaryotic editing and mutagenic nucleic acid deaminases from bacterial toxin systems. PUBMED:21890906 EPMC:21890906

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR002466

Editase (EC) are enzymes that alter mRNA by catalyzing the site-selective deamination of adenosine residue into inosine residue. The editase domain contains the active site and binds three Zn atoms [PUBMED:9159072].

Several editases share a common global arrangement of domains, from N to C terminus: two 'double-stranded RNA-specific adenosine deaminase' (DRADA) repeat domains (INTERPRO), followed by three 'double-stranded RNA binding' (DsRBD) domains, followed by the editase domain. Other editases have a simplified domains structure with no DRADA_REP and possibly fewer DSRBD domains. Editase that deaminate cytidine are not detected by this signature.

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Domain organisation

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Pfam Clan

This family is a member of clan CDA (CL0109), which has the following description:

This clan contains both free nucleotide and nucleic acid deaminases that act on adenosine, cytosine, guanine and cytidine, and are collectively known as the deaminase superfamily. The conserved fold consists of a three-layered alpha/beta/alpha structure with 3 helices and 4 strands in the 2134 order [1,2].This superfamily is further divided into two major divisions based on the presence of a helix (helix-4) that renders the terminal strands (strands 4 and 5) either parallel to each other in its presence, or anti-parallel in its absence [2]. Structurally, the deaminase-like fold is present in four other superfamilies including the JAB-like metalloproteins, the C-terminal AICAR transformylase-catalyzing domains of PurH, Tm1506 and the formate dehydrogenase accessory subunit FdhD. The active site of the deaminases is composed of three residues that coordinate a zinc ion between conserved helices 2 and 3. The residues are typically found as [HCD]xE and CxxC motifs at the beginning of helices 2 and 3. The zinc ion activates a water molecule, which forms a tetrahderal intermediate with the carbon atom that is linked to the amine group. This is followed by deamination of the base.

The clan contains the following 33 members:

A_deamin AICARFT_IMPCHas AID APOBEC1 APOBEC2 APOBEC3 APOBEC4 APOBEC4_like APOBEC_C APOBEC_N Bd3614-deam DAAD dCMP_cyt_deam_1 dCMP_cyt_deam_2 DYW_deaminase FdhD-NarQ Inv-AAD LmjF365940-deam LpxI_C MafB19-deam NAD1 NAD2 OTT_1508_deam Pput2613-deam SCP1201-deam SNAD1 SNAD2 SNAD3 SNAD4 TM1506 Toxin-deaminase XOO_2897-deam YwqJ-deaminase


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Curation and family details

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Curation View help on the curation process

Seed source: IPR002466
Previous IDs: none
Type: Family
Sequence Ontology: SO:0100021
Author: Mian N , Bateman A , Iyer LM , Zhang D , Aravind L
Number in seed: 98
Number in full: 2269
Average length of the domain: 277.50 aa
Average identity of full alignment: 26 %
Average coverage of the sequence by the domain: 54.60 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 45638612 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 19.8 19.8
Trusted cut-off 20.3 19.9
Noise cut-off 19.6 19.7
Model length: 329
Family (HMM) version: 18
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Archea Archea Eukaryota Eukaryota
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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 A_deamin domain has been found. There are 10 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.

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