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0  structures 777  species 0  interactions 866  sequences 7  architectures

Family: DUF521 (PF04412)

Summary: Protein of unknown function (DUF521)

Pfam includes annotations and additional family information from a range of different sources. These sources can be accessed via the tabs below.

This is the Wikipedia entry entitled "Aconitase". More...

Aconitase Edit Wikipedia article

aconitate hydratase
7ACN.jpg
Illustration of pig aconitase in complex with the [Fe4S4] cluster. The protein is colored by secondary structure, and iron atoms are blue and the sulfur red.[1]
Identifiers
EC number4.2.1.3
CAS number9024-25-3
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO
Aconitase family
(aconitate hydratase)
PDB 1aco EBI.jpg
Structure of aconitase.[2]
Identifiers
SymbolAconitase
PfamPF00330
InterProIPR001030
PROSITEPDOC00423
SCOPe1aco / SUPFAM

Aconitase (aconitate hydratase; EC 4.2.1.3) is an enzyme that catalyses the stereo-specific isomerization of citrate to isocitrate via cis-aconitate in the tricarboxylic acid cycle, a non-redox-active process.[3][4][5]

Structure

Aconitase, displayed in the structures in the right margin of this page, has two slightly different structures, depending on whether it is activated or inactivated.[6][7] In the inactive form, its structure is divided into four domains.[6] Counting from the N-terminus, only the first three of these domains are involved in close interactions with the [3Fe-4S] cluster, but the active site consists of residues from all four domains, including the larger C-terminal domain.[6] The Fe-S cluster and a SO42− anion also reside in the active site.[6] When the enzyme is activated, it gains an additional iron atom, creating a [4Fe-4S] cluster.[7][8] However, the structure of the rest of the enzyme is nearly unchanged; the conserved atoms between the two forms are in essentially the same positions, up to a difference of 0.1 angstroms.[7]

Function

In contrast with the majority of iron-sulfur proteins that function as electron carriers, the iron-sulfur cluster of aconitase reacts directly with an enzyme substrate. Aconitase has an active [Fe4S4]2+ cluster, which may convert to an inactive [Fe3S4]+ form. Three cysteine (Cys) residues have been shown to be ligands of the [Fe4S4] centre. In the active state, the labile iron ion of the [Fe4S4] cluster is not coordinated by Cys but by water molecules.

The iron-responsive element-binding protein (IRE-BP) and 3-isopropylmalate dehydratase (α-isopropylmalate isomerase; EC 4.2.1.33), an enzyme catalysing the second step in the biosynthesis of leucine, are known aconitase homologues. Iron regulatory elements (IREs) constitute a family of 28-nucleotide, non-coding, stem-loop structures that regulate iron storage, heme synthesis and iron uptake. They also participate in ribosome binding and control the mRNA turnover (degradation). The specific regulator protein, the IRE-BP, binds to IREs in both 5' and 3' regions, but only to RNA in the apo form, without the Fe-S cluster. Expression of IRE-BP in cultured cells has revealed that the protein functions either as an active aconitase, when cells are iron-replete, or as an active RNA-binding protein, when cells are iron-depleted. Mutant IRE-BPs, in which any or all of the three Cys residues involved in Fe-S formation are replaced by serine, have no aconitase activity, but retain RNA-binding properties.

Aconitase is inhibited by fluoroacetate, therefore fluoroacetate is poisonous. Fluoroacetate, in the citric acid cycle, can innocently enter as fluorocitrate. However, aconitase cannot bind this substrate and thus the citric acid cycle is halted. The iron sulfur cluster is highly sensitive to oxidation by superoxide.[9]

Mechanism

Aconitase arrow-pushing mechanism [10][11]
Citrate and the Fe-S cluster in the active site of aconitase: dashed yellow lines show interactions between the substrate and nearby residues[12]

Aconitase employs a dehydration-hydration mechanism.[10] The catalytic residues involved are His-101 and Ser-642.[10] His-101 protonates the hydroxyl group on C3 of citrate, allowing it to leave as water, and Ser-642 concurrently abstracts the proton on C2, forming a double bond between C2 and C3, forming a cis-aconitate intermediate.[10][13] At this point, the intermediate is rotated 180°.[10] This rotation is referred to as a "flip."[11] Because of this flip, the intermediate is said to move from a "citrate mode" to a "isocitrate mode."[14]

How exactly this flip occurs is debatable. One theory is that, in the rate-limiting step of the mechanism, the cis-aconitate is released from the enzyme, then reattached in the isocitrate mode to complete the reaction.[14] This rate-limiting step ensures that the right stereochemistry, specifically (2R,3S), is formed in the final product.[14][15] Another hypothesis is that cis-aconitate stays bound to the enzyme while it flips from the citrate to the isocitrate mode.[10]

In either case, flipping cis-aconitate allows the dehydration and hydration steps to occur on opposite faces of the intermediate.[10] Aconitase catalyzes trans elimination/addition of water, and the flip guarantees that the correct stereochemistry is formed in the product.[10][11] To complete the reaction, the serine and histidine residues reverse their original catalytic actions: the histidine, now basic, abstracts a proton from water, priming it as a nucleophile to attack at C2, and the protonated serine is deprotonated by the cis-aconitate double bond to complete the hydration, producing isocitrate.[10]

Isocitrate and the Fe-S cluster in the active site of aconitase[12]PDB: 1C97​;

Family members

Aconitases are expressed in bacteria to humans. Humans express the following two aconitase isozymes:

aconitase 1, soluble
Identifiers
SymbolACO1
Alt. symbolsIREB1
NCBI gene48
HGNC117
OMIM100880
RefSeqNM_002197
UniProtP21399
Other data
EC number4.2.1.3
LocusChr. 9 p21.1
aconitase 2, mitochondrial
Identifiers
SymbolACO2
Alt. symbolsACONM
NCBI gene50
HGNC118
OMIM100850
RefSeqNM_001098
UniProtQ99798
Other data
EC number4.2.1.3
LocusChr. 22 q13.2

Interactive pathway map

Click on genes, proteins and metabolites below to link to respective articles. [§ 1]

[[File:
TCACycle_WP78go to articlego to articlego to articlego to articlego to HMDBgo to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to HMDBgo to articlego to articlego to HMDBgo to articlego to articlego to HMDBgo to articlego to articlego to HMDBgo to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to WikiPathwaysgo to articlego to articlego to articlego to article
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TCACycle_WP78go to articlego to articlego to articlego to articlego to HMDBgo to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to HMDBgo to articlego to articlego to HMDBgo to articlego to articlego to HMDBgo to articlego to articlego to HMDBgo to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to articlego to WikiPathwaysgo to articlego to articlego to articlego to article
|{{{bSize}}}px|alt=TCA Cycle edit]]
TCA Cycle edit
  1. ^ The interactive pathway map can be edited at WikiPathways: "TCACycle_WP78".

References

  1. ^ PDB: 7ACN​; Lauble, H.; Kennedy, M. C.; Beinert, H.; Stout, C. D. (1992). "Crystal structures of aconitase with isocitrate and nitroisocitrate bound". Biochemistry. 31 (10): 2735–48. doi:10.1021/bi00125a014. PMID 1547214.
  2. ^ PDB: 1ACO​; Lauble, H; Kennedy, MC; Beinert, H; Stout, CD (1994). "Crystal Structures of Aconitase with Trans-aconitate and Nitrocitrate Bound". Journal of Molecular Biology. 237 (4): 437–51. doi:10.1006/jmbi.1994.1246. PMID 8151704.
  3. ^ Beinert H, Kennedy MC (Dec 1993). "Aconitase, a two-faced protein: enzyme and iron regulatory factor". FASEB Journal. 7 (15): 1442–9. PMID 8262329.
  4. ^ Flint, Dennis H.; Allen, Ronda M. (1996). "Iron−Sulfur Proteins with Nonredox Functions". Chemical Reviews. 96 (7): 2315–34. doi:10.1021/cr950041r.
  5. ^ Beinert H, Kennedy MC, Stout CD (Nov 1996). "Aconitase as Ironminus signSulfur Protein, Enzyme, and Iron-Regulatory Protein". Chemical Reviews. 96 (7): 2335–2374. doi:10.1021/cr950040z. PMID 11848830.
  6. ^ a b c d Robbins AH, Stout CD (1989). "The structure of aconitase". Proteins. 5 (4): 289–312. doi:10.1002/prot.340050406. PMID 2798408.
  7. ^ a b c Robbins AH, Stout CD (May 1989). "Structure of activated aconitase: formation of the [4Fe-4S] cluster in the crystal". Proceedings of the National Academy of Sciences of the United States of America. 86 (10): 3639–43. doi:10.1073/pnas.86.10.3639. PMC 287193. PMID 2726740.
  8. ^ Lauble H, Kennedy MC, Beinert H, Stout CD (Mar 1992). "Crystal structures of aconitase with isocitrate and nitroisocitrate bound". Biochemistry. 31 (10): 2735–48. doi:10.1021/bi00125a014. PMID 1547214.
  9. ^ Gardner, Paul R. (2002). "Aconitase: Sensitive target and measure of superoxide". Superoxide Dismutase. Methods in Enzymology. 349. pp. 9–23. doi:10.1016/S0076-6879(02)49317-2. ISBN 978-0-12-182252-1.
  10. ^ a b c d e f g h i Takusagawa F. "Chapter 16: Citric Acid Cycle" (PDF). Takusagawa’s Note. The University of Kansas. Archived from the original (PDF) on 2012-03-24. Retrieved 2011-07-10.
  11. ^ a b c Beinert H, Kennedy MC, Stout CD (Nov 1996). "Aconitase as Ironminus signSulfur Protein, Enzyme, and Iron-Regulatory Protein" (PDF). Chemical Reviews. 96 (7): 2335–2374. doi:10.1021/cr950040z. PMID 11848830. Archived from the original (PDF) on 2011-08-11. Retrieved 2011-05-16.
  12. ^ a b PDB: 1C96​; Lloyd SJ, Lauble H, Prasad GS, Stout CD (December 1999). "The mechanism of aconitase: 1.8 A resolution crystal structure of the S642a:citrate complex". Protein Sci. 8 (12): 2655–62. doi:10.1110/ps.8.12.2655. PMC 2144235. PMID 10631981.
  13. ^ Han D, Canali R, Garcia J, Aguilera R, Gallaher TK, Cadenas E (Sep 2005). "Sites and mechanisms of aconitase inactivation by peroxynitrite: modulation by citrate and glutathione". Biochemistry. 44 (36): 11986–96. doi:10.1021/bi0509393. PMID 16142896.
  14. ^ a b c Lauble H, Stout CD (May 1995). "Steric and conformational features of the aconitase mechanism". Proteins. 22 (1): 1–11. doi:10.1002/prot.340220102. PMID 7675781.
  15. ^ "Aconitase family". The Prosthetic groups and Metal Ions in Protein Active Sites Database Version 2.0. The University of Leeds. 1999-02-02. Archived from the original on 2011-06-08. Retrieved 2011-07-10.

Further reading

  • Frishman D, Hentze MW (Jul 1996). "Conservation of aconitase residues revealed by multiple sequence analysis. Implications for structure/function relationships". European Journal of Biochemistry / FEBS. 239 (1): 197–200. doi:10.1111/j.1432-1033.1996.0197u.x. PMID 8706708.

External links

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

This is the Wikipedia entry entitled "Domain of unknown function". More...

Domain of unknown function Edit Wikipedia article

A domain of unknown function (DUF) is a protein domain that has no characterised function. These families have been collected together in the Pfam database using the prefix DUF followed by a number, with examples being DUF2992 and DUF1220. As of 2019, there are almost 4,000 DUF families within the Pfam database representing over 22% of known families. Some DUFs are not named using the nomenclature due to popular usage but are nevertheless DUFs.[1]

The DUF designation is tentative, and such families tend to be renamed to a more specific name (or merged to an existing domain) after a function is identified.[2][3]

History

The DUF naming scheme was introduced by Chris Ponting, through the addition of DUF1 and DUF2 to the SMART database.[4] These two domains were found to be widely distributed in bacterial signaling proteins. Subsequently, the functions of these domains were identified and they have since been renamed as the GGDEF domain and EAL domain respectively.[2]

Characterisation

Structural genomics programmes have attempted to understand the function of DUFs through structure determination. The structures of over 250 DUF families have been solved. This (2009) work showed that about two thirds of DUF families had a structure similar to a previously solved one and therefore likely to be divergent members of existing protein superfamilies, whereas about one third possessed a novel protein fold.[5]

Some DUF families share remote sequence homology with domains that has characterized function. Computational work can be used to link these relationships. An 2015 work was able to assign 20% of the DUFs to characterized structual superfamilies.[6] Pfam also continuously perform the (manually-verified) assignment in "clan" superfamily entries.[1]

Frequency and conservation

Protein domains and DUFs in different domains of life. Left: Annotated domains. Right: domains of unknown function. Not all overlaps shown.[7]

More than 20% of all protein domains were annotated as DUFs in 2013. About 2,700 DUFs are found in bacteria compared with just over 1,500 in eukaryotes. Over 800 DUFs are shared between bacteria and eukaryotes, and about 300 of these are also present in archaea. A total of 2,786 bacterial Pfam domains even occur in animals, including 320 DUFs.[7]

Role in biology

Many DUFs are highly conserved, indicating an important role in biology. However, many such DUFs are not essential, hence their biological role often remains unknown. For instance, DUF143 is present in most bacteria and eukaryotic genomes.[8] However, when it was deleted in Escherichia coli no obvious phenotype was detected. Later it was shown that the proteins that contain DUF143, are ribosomal silencing factors that block the assembly of the two ribosomal subunits.[8] While this function is not essential, it helps the cells to adapt to low nutrient conditions by shutting down protein biosynthesis. As a result, these proteins and the DUF only become relevant when the cells starve.[8] It is thus believed that many DUFs (or proteins of unknown function, PUFs) are only required under certain conditions.

Essential DUFs

Goodacre et al. identified 238 DUFs in 355 essential proteins (in 16 model bacterial species), most of which represent single-domain proteins, clearly establishing the biological essentiality of DUFs. These DUFs are called "essential DUFs" or eDUFs.[7]

External links

References

  1. ^ a b El-Gebali S, Mistry J, Bateman A, Eddy SR, Luciani A, Potter SC, Qureshi M, Richardson LJ, Salazar GA, Smart A, Sonnhammer EL, Hirsh L, Paladin L, Piovesan D, Tosatto SC, Finn RD (January 2019). "The Pfam protein families database in 2019". Nucleic Acids Research. 47 (D1): D427–D432. doi:10.1093/nar/gky995. PMC 6324024. PMID 30357350.
  2. ^ a b Bateman A, Coggill P, Finn RD (October 2010). "DUFs: families in search of function". Acta Crystallographica. Section F, Structural Biology and Crystallization Communications. 66 (Pt 10): 1148–52. doi:10.1107/S1744309110001685. PMC 2954198. PMID 20944204.
  3. ^ Punta M, Coggill PC, Eberhardt RY, Mistry J, Tate J, Boursnell C, Pang N, Forslund K, Ceric G, Clements J, Heger A, Holm L, Sonnhammer EL, Eddy SR, Bateman A, Finn RD (January 2012). "The Pfam protein families database". Nucleic Acids Research. 40 (Database issue): D290–301. doi:10.1093/nar/gkr1065. PMC 3245129. PMID 22127870.
  4. ^ Schultz J, Milpetz F, Bork P, Ponting CP (May 1998). "SMART, a simple modular architecture research tool: identification of signaling domains". Proceedings of the National Academy of Sciences of the United States of America. 95 (11): 5857–64. Bibcode:1998PNAS...95.5857S. doi:10.1073/pnas.95.11.5857. PMC 34487. PMID 9600884.
  5. ^ Jaroszewski L, Li Z, Krishna SS, Bakolitsa C, Wooley J, Deacon AM, Wilson IA, Godzik A (September 2009). "Exploration of uncharted regions of the protein universe". PLoS Biology. 7 (9): e1000205. doi:10.1371/journal.pbio.1000205. PMC 2744874. PMID 19787035.
  6. ^ Mudgal R, Sandhya S, Chandra N, Srinivasan N (July 2015). "De-DUFing the DUFs: Deciphering distant evolutionary relationships of Domains of Unknown Function using sensitive homology detection methods". Biology Direct. 10 (1): 38. doi:10.1186/s13062-015-0069-2. PMC 4520260. PMID 26228684.
  7. ^ a b c Goodacre NF, Gerloff DL, Uetz P (December 2013). "Protein domains of unknown function are essential in bacteria". mBio. 5 (1): e00744–13. doi:10.1128/mBio.00744-13. PMC 3884060. PMID 24381303.
  8. ^ a b c Häuser R, Pech M, Kijek J, Yamamoto H, Titz B, Naeve F, Tovchigrechko A, Yamamoto K, Szaflarski W, Takeuchi N, Stellberger T, Diefenbacher ME, Nierhaus KH, Uetz P (2012). Hughes D (ed.). "RsfA (YbeB) proteins are conserved ribosomal silencing factors". PLoS Genetics. 8 (7): e1002815. doi:10.1371/journal.pgen.1002815. PMC 3400551. PMID 22829778.

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

"DUF" families are annotated with the Domain of unknown function Wikipedia article. This is a general article, with no specific information about individual Pfam DUFs. If you have information about this particular DUF, please let us know using the "Add annotation" button below.

Protein of unknown function (DUF521) Provide feedback

Family of hypothetical proteins.

Internal database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR007506

This putative aconitase X catalytic domain is predicted by comparative genomic analysis. The proteins are mainly found in archaea and proteobacteria. They are distantly related to Aconitase family of proteins by sequence similarity and seconary structure prediction. The functions have not yet been experimentally characterized. Thus, the prediction should be treated with caution [PUBMED:14568143].

Domain organisation

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Alignments

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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.

  Seed
(120)
Full
(866)
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(2543)
NCBI
(3341)
Meta
(336)
RP15
(240)
RP35
(533)
RP55
(798)
RP75
(1215)
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Key: ✓ available, x not generated, not available.

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(120)
Full
(866)
Representative proteomes UniProt
(2543)
NCBI
(3341)
Meta
(336)
RP15
(240)
RP35
(533)
RP55
(798)
RP75
(1215)
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  Seed
(120)
Full
(866)
Representative proteomes UniProt
(2543)
NCBI
(3341)
Meta
(336)
RP15
(240)
RP35
(533)
RP55
(798)
RP75
(1215)
Raw Stockholm Download   Download   Download   Download   Download   Download   Download   Download   Download  
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You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

HMM logo

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...

Trees

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.

Curation View help on the curation process

Seed source: COG1679
Previous IDs: none
Type: Family
Sequence Ontology: SO:0100021
Author: Waterfield DI , Finn RD
Number in seed: 120
Number in full: 866
Average length of the domain: 386.70 aa
Average identity of full alignment: 33 %
Average coverage of the sequence by the domain: 86.23 %

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 31.5 31.5
Trusted cut-off 33.9 31.6
Noise cut-off 31.4 30.4
Model length: 401
Family (HMM) version: 13
Download: download the raw HMM for this family

Species distribution

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