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Protein

Isocitrate dehydrogenase [NADP]

Gene

icd

Organism
Escherichia coli (strain K12)
Status
Reviewed-Annotation score: Annotation score: 5 out of 5-Experimental evidence at protein leveli

Functioni

Catalytic activityi

Isocitrate + NADP+ = 2-oxoglutarate + CO2 + NADPH.1 Publication

Cofactori

Mg2+, Mn2+Note: Binds 1 Mg(2+) or Mn2+ ion per subunit.

Enzyme regulationi

Inhibition of this enzyme by phosphorylation regulates the branch point between the Krebs cycle and the glyoxylate bypass, which is an alternate route that accumulates carbon for biosynthesis when acetate is the sole carbon source for growth.

Kineticsi

  1. KM=11.4 µM for isocitrate1 Publication

Sites

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Binding sitei104 – 1041NADP3 Publications
Binding sitei113 – 1131Substrate1 Publication
Binding sitei115 – 1151Substrate
Binding sitei119 – 1191Substrate
Binding sitei129 – 1291Substrate
Binding sitei153 – 1531Substrate
Sitei160 – 1601Critical for catalysis
Sitei230 – 2301Critical for catalysis
Metal bindingi307 – 3071Magnesium or manganese3 Publications
Binding sitei352 – 3521NADP; via amide nitrogen and carbonyl oxygen3 Publications
Binding sitei391 – 3911NADP3 Publications
Binding sitei395 – 3951NADP3 Publications

Regions

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Nucleotide bindingi339 – 3457NADP3 Publications

GO - Molecular functioni

  1. isocitrate dehydrogenase (NADP+) activity Source: UniProtKB
  2. magnesium ion binding Source: InterPro
  3. NAD binding Source: InterPro

GO - Biological processi

  1. electron transport chain Source: EcoliWiki
  2. glyoxylate cycle Source: UniProtKB-KW
  3. response to oxidative stress Source: EcoCyc
  4. tricarboxylic acid cycle Source: UniProtKB-KW
Complete GO annotation...

Keywords - Molecular functioni

Oxidoreductase

Keywords - Biological processi

Glyoxylate bypass, Tricarboxylic acid cycle

Keywords - Ligandi

Magnesium, Manganese, Metal-binding, NADP

Enzyme and pathway databases

BioCyciEcoCyc:ISOCITDEH-SUBUNIT.
ECOL316407:JW1122-MONOMER.
MetaCyc:ISOCITDEH-SUBUNIT.
SABIO-RKP08200.

Names & Taxonomyi

Protein namesi
Recommended name:
Isocitrate dehydrogenase [NADP] (EC:1.1.1.42)
Short name:
IDH
Alternative name(s):
IDP
NADP(+)-specific ICDH
Oxalosuccinate decarboxylase
Gene namesi
Name:icd
Synonyms:icdA, icdE
Ordered Locus Names:b1136, JW1122
OrganismiEscherichia coli (strain K12)
Taxonomic identifieri83333 [NCBI]
Taxonomic lineageiBacteriaProteobacteriaGammaproteobacteriaEnterobacterialesEnterobacteriaceaeEscherichia
ProteomesiUP000000318: Chromosome, UP000000625: Chromosome

Organism-specific databases

EcoGeneiEG10489. icd.
EG10009. icdC.

Subcellular locationi

GO - Cellular componenti

  1. cytoplasm Source: EcoliWiki
Complete GO annotation...

Pathology & Biotechi

Mutagenesis

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Mutagenesisi100 – 1001K → R or E: Abolishes enzymatic activity. 1 Publication
Mutagenesisi113 – 1131S → D or E: Reduced affinity for isocitrate. 1 Publication
Mutagenesisi160 – 1601Y → F: Large decrease in activity and a small increase in substrate affinity. 2 Publications
Mutagenesisi230 – 2301K → M: Decrease in activity and substrate affinity. 2 Publications
Mutagenesisi242 – 2421K → E: Strongly impairs enzymatic activity. 1 Publication
Mutagenesisi242 – 2421K → R: Impairs enzymatic activity. 1 Publication

PTM / Processingi

Molecule processing

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Chaini1 – 416416Isocitrate dehydrogenase [NADP]PRO_0000083551Add
BLAST

Amino acid modifications

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Modified residuei100 – 1001N6-succinyllysine1 Publication
Modified residuei113 – 1131Phosphoserine1 Publication
Modified residuei142 – 1421N6-acetyllysine1 Publication
Modified residuei242 – 2421N6-succinyllysine1 Publication

Post-translational modificationi

Phosphorylation state of this enzyme is controlled by isocitrate dehydrogenase kinase/phosphatase (AceK).1 Publication
Succinylation probably inhibits enzymatic activity.1 Publication

Keywords - PTMi

Acetylation, Phosphoprotein

Proteomic databases

PaxDbiP08200.
PRIDEiP08200.

2D gel databases

SWISS-2DPAGEP08200.

Expressioni

Gene expression databases

GenevestigatoriP08200.

Interactioni

Subunit structurei

Homodimer.4 Publications

Protein-protein interaction databases

DIPiDIP-10006N.
IntActiP08200. 6 interactions.
STRINGi511145.b1136.

Structurei

Secondary structure

1
416
Legend: HelixTurnBeta strand
Show more details
Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Beta strandi15 – 173Combined sources
Beta strandi20 – 223Combined sources
Beta strandi25 – 328Combined sources
Helixi38 – 5720Combined sources
Beta strandi58 – 614Combined sources
Beta strandi64 – 674Combined sources
Helixi72 – 787Combined sources
Helixi86 – 9510Combined sources
Beta strandi96 – 1005Combined sources
Beta strandi107 – 1093Combined sources
Helixi114 – 1218Combined sources
Beta strandi126 – 1327Combined sources
Beta strandi140 – 1423Combined sources
Helixi144 – 1463Combined sources
Beta strandi148 – 1547Combined sources
Helixi158 – 1614Combined sources
Beta strandi163 – 1653Combined sources
Helixi170 – 18112Combined sources
Beta strandi196 – 1983Combined sources
Helixi203 – 21917Combined sources
Beta strandi223 – 2297Combined sources
Turni231 – 2333Combined sources
Turni235 – 2373Combined sources
Helixi238 – 25316Combined sources
Beta strandi256 – 2583Combined sources
Beta strandi259 – 2624Combined sources
Beta strandi264 – 2674Combined sources
Turni269 – 2713Combined sources
Beta strandi274 – 2818Combined sources
Helixi282 – 29110Combined sources
Helixi293 – 2953Combined sources
Beta strandi298 – 3014Combined sources
Helixi303 – 31614Combined sources
Turni320 – 3223Combined sources
Beta strandi326 – 3283Combined sources
Beta strandi333 – 3364Combined sources
Helixi343 – 3453Combined sources
Turni346 – 3494Combined sources
Helixi354 – 36613Combined sources
Helixi370 – 38516Combined sources
Beta strandi388 – 3903Combined sources
Helixi391 – 3944Combined sources
Beta strandi397 – 3993Combined sources
Beta strandi401 – 4033Combined sources
Helixi405 – 41410Combined sources

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
EntryMethodResolution (Å)ChainPositionsPDBsum
1AI2X-ray1.90A1-416[»]
1AI3X-ray1.90A1-416[»]
1BL5X-ray2.50A3-416[»]
1CW1X-ray2.10A1-416[»]
1CW4X-ray2.10A1-416[»]
1CW7X-ray2.60A1-416[»]
1GROX-ray2.50A1-416[»]
1GRPX-ray2.50A1-416[»]
1HJ6X-ray2.00A1-416[»]
1IDCX-ray2.50A1-416[»]
1IDDX-ray2.50A1-416[»]
1IDEX-ray2.50A1-416[»]
1IDFX-ray2.50A1-416[»]
1IKAX-ray2.70A1-416[»]
1ISOX-ray1.90A1-416[»]
1P8FX-ray1.85A1-416[»]
1PB1X-ray1.70A1-416[»]
1PB3X-ray1.70A1-416[»]
1SJSX-ray2.42A1-416[»]
3ICDX-ray2.50A1-416[»]
3LCBX-ray2.90C/D1-416[»]
4AJ3X-ray1.90A1-416[»]
4AJAX-ray1.80A1-416[»]
4AJBX-ray1.90A1-416[»]
4AJCX-ray2.30A1-416[»]
4AJRX-ray2.69A1-416[»]
4AJSX-ray1.80A1-416[»]
4BNPX-ray2.00A1-416[»]
4ICDX-ray2.50A1-416[»]
4P69X-ray3.30C/D2-416[»]
5ICDX-ray2.50A1-416[»]
6ICDX-ray2.80A1-416[»]
7ICDX-ray2.40A1-416[»]
8ICDX-ray2.50A1-416[»]
9ICDX-ray2.50A1-416[»]
ProteinModelPortaliP08200.
SMRiP08200. Positions 1-416.
ModBaseiSearch...
MobiDBiSearch...

Miscellaneous databases

EvolutionaryTraceiP08200.

Family & Domainsi

Sequence similaritiesi

Phylogenomic databases

eggNOGiCOG0538.
HOGENOMiHOG000021113.
InParanoidiP08200.
KOiK00031.
OMAiFRDWGYE.
OrthoDBiEOG6SNDTP.
PhylomeDBiP08200.

Family and domain databases

Gene3Di3.40.718.10. 1 hit.
InterProiIPR019818. IsoCit/isopropylmalate_DH_CS.
IPR001804. Isocitrate/isopropylmalate_DH.
IPR004439. Isocitrate_DH_NADP_dimer_prok.
IPR024084. IsoPropMal-DH-like_dom.
[Graphical view]
PANTHERiPTHR11835. PTHR11835. 1 hit.
PfamiPF00180. Iso_dh. 1 hit.
[Graphical view]
TIGRFAMsiTIGR00183. prok_nadp_idh. 1 hit.
PROSITEiPS00470. IDH_IMDH. 1 hit.
[Graphical view]

Sequencei

Sequence statusi: Complete.

P08200-1 [UniParc]FASTAAdd to basket

« Hide

        10         20         30         40         50
MESKVVVPAQ GKKITLQNGK LNVPENPIIP YIEGDGIGVD VTPAMLKVVD
60 70 80 90 100
AAVEKAYKGE RKISWMEIYT GEKSTQVYGQ DVWLPAETLD LIREYRVAIK
110 120 130 140 150
GPLTTPVGGG IRSLNVALRQ ELDLYICLRP VRYYQGTPSP VKHPELTDMV
160 170 180 190 200
IFRENSEDIY AGIEWKADSA DAEKVIKFLR EEMGVKKIRF PEHCGIGIKP
210 220 230 240 250
CSEEGTKRLV RAAIEYAIAN DRDSVTLVHK GNIMKFTEGA FKDWGYQLAR
260 270 280 290 300
EEFGGELIDG GPWLKVKNPN TGKEIVIKDV IADAFLQQIL LRPAEYDVIA
310 320 330 340 350
CMNLNGDYIS DALAAQVGGI GIAPGANIGD ECALFEATHG TAPKYAGQDK
360 370 380 390 400
VNPGSIILSA EMMLRHMGWT EAADLIVKGM EGAINAKTVT YDFERLMDGA
410
KLLKCSEFGD AIIENM
Length:416
Mass (Da):45,757
Last modified:August 1, 1988 - v1
Checksum:i9A02E707C3B4FDD9
GO

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
J02799 Genomic DNA. Translation: AAA24006.1.
U00096 Genomic DNA. Translation: AAC74220.1.
AP009048 Genomic DNA. Translation: BAA35958.1.
AF017587 Genomic DNA. Translation: AAC45887.1.
PIRiA28482. DCECIS.
RefSeqiNP_415654.1. NC_000913.3.
YP_489404.1. NC_007779.1.

Genome annotation databases

EnsemblBacteriaiAAC74220; AAC74220; b1136.
BAA35958; BAA35958; BAA35958.
GeneIDi12934062.
945702.
KEGGiecj:Y75_p1106.
eco:b1136.
PATRICi32117521. VBIEscCol129921_1183.

Cross-referencesi

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
J02799 Genomic DNA. Translation: AAA24006.1.
U00096 Genomic DNA. Translation: AAC74220.1.
AP009048 Genomic DNA. Translation: BAA35958.1.
AF017587 Genomic DNA. Translation: AAC45887.1.
PIRiA28482. DCECIS.
RefSeqiNP_415654.1. NC_000913.3.
YP_489404.1. NC_007779.1.

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
EntryMethodResolution (Å)ChainPositionsPDBsum
1AI2X-ray1.90A1-416[»]
1AI3X-ray1.90A1-416[»]
1BL5X-ray2.50A3-416[»]
1CW1X-ray2.10A1-416[»]
1CW4X-ray2.10A1-416[»]
1CW7X-ray2.60A1-416[»]
1GROX-ray2.50A1-416[»]
1GRPX-ray2.50A1-416[»]
1HJ6X-ray2.00A1-416[»]
1IDCX-ray2.50A1-416[»]
1IDDX-ray2.50A1-416[»]
1IDEX-ray2.50A1-416[»]
1IDFX-ray2.50A1-416[»]
1IKAX-ray2.70A1-416[»]
1ISOX-ray1.90A1-416[»]
1P8FX-ray1.85A1-416[»]
1PB1X-ray1.70A1-416[»]
1PB3X-ray1.70A1-416[»]
1SJSX-ray2.42A1-416[»]
3ICDX-ray2.50A1-416[»]
3LCBX-ray2.90C/D1-416[»]
4AJ3X-ray1.90A1-416[»]
4AJAX-ray1.80A1-416[»]
4AJBX-ray1.90A1-416[»]
4AJCX-ray2.30A1-416[»]
4AJRX-ray2.69A1-416[»]
4AJSX-ray1.80A1-416[»]
4BNPX-ray2.00A1-416[»]
4ICDX-ray2.50A1-416[»]
4P69X-ray3.30C/D2-416[»]
5ICDX-ray2.50A1-416[»]
6ICDX-ray2.80A1-416[»]
7ICDX-ray2.40A1-416[»]
8ICDX-ray2.50A1-416[»]
9ICDX-ray2.50A1-416[»]
ProteinModelPortaliP08200.
SMRiP08200. Positions 1-416.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

DIPiDIP-10006N.
IntActiP08200. 6 interactions.
STRINGi511145.b1136.

2D gel databases

SWISS-2DPAGEP08200.

Proteomic databases

PaxDbiP08200.
PRIDEiP08200.

Protocols and materials databases

Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsemblBacteriaiAAC74220; AAC74220; b1136.
BAA35958; BAA35958; BAA35958.
GeneIDi12934062.
945702.
KEGGiecj:Y75_p1106.
eco:b1136.
PATRICi32117521. VBIEscCol129921_1183.

Organism-specific databases

EchoBASEiEB0484.
EcoGeneiEG10489. icd.
EG10009. icdC.

Phylogenomic databases

eggNOGiCOG0538.
HOGENOMiHOG000021113.
InParanoidiP08200.
KOiK00031.
OMAiFRDWGYE.
OrthoDBiEOG6SNDTP.
PhylomeDBiP08200.

Enzyme and pathway databases

BioCyciEcoCyc:ISOCITDEH-SUBUNIT.
ECOL316407:JW1122-MONOMER.
MetaCyc:ISOCITDEH-SUBUNIT.
SABIO-RKP08200.

Miscellaneous databases

EvolutionaryTraceiP08200.
PROiP08200.

Gene expression databases

GenevestigatoriP08200.

Family and domain databases

Gene3Di3.40.718.10. 1 hit.
InterProiIPR019818. IsoCit/isopropylmalate_DH_CS.
IPR001804. Isocitrate/isopropylmalate_DH.
IPR004439. Isocitrate_DH_NADP_dimer_prok.
IPR024084. IsoPropMal-DH-like_dom.
[Graphical view]
PANTHERiPTHR11835. PTHR11835. 1 hit.
PfamiPF00180. Iso_dh. 1 hit.
[Graphical view]
TIGRFAMsiTIGR00183. prok_nadp_idh. 1 hit.
PROSITEiPS00470. IDH_IMDH. 1 hit.
[Graphical view]
ProtoNetiSearch...

Publicationsi

« Hide 'large scale' publications
  1. "Inactivation of isocitrate dehydrogenase by phosphorylation is mediated by the negative charge of the phosphate."
    Thorsness P.E., Koshland D.E. Jr.
    J. Biol. Chem. 262:10422-10425(1987) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [GENOMIC DNA].
  2. Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
    Strain: K12 / W3110 / ATCC 27325 / DSM 5911.
  3. Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
    Strain: K12 / MG1655 / ATCC 47076.
  4. "Highly accurate genome sequences of Escherichia coli K-12 strains MG1655 and W3110."
    Hayashi K., Morooka N., Yamamoto Y., Fujita K., Isono K., Choi S., Ohtsubo E., Baba T., Wanner B.L., Mori H., Horiuchi T.
    Mol. Syst. Biol. 2:E1-E5(2006) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
    Strain: K12 / W3110 / ATCC 27325 / DSM 5911.
  5. "Evolutionary genetics of the isocitrate dehydrogenase gene (icd) in Escherichia coli and Salmonella enterica."
    Wang F.-S., Whittam T.S., Selander R.K.
    J. Bacteriol. 179:6551-6559(1997) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [GENOMIC DNA] OF 11-414.
    Strain: CH734.
  6. "Comparing the predicted and observed properties of proteins encoded in the genome of Escherichia coli K-12."
    Link A.J., Robison K., Church G.M.
    Electrophoresis 18:1259-1313(1997) [PubMed] [Europe PMC] [Abstract]
    Cited for: PROTEIN SEQUENCE OF 1-12.
    Strain: K12 / EMG2.
  7. "Mutational analysis of the catalytic residues lysine 230 and tyrosine 160 in the NADP(+)-dependent isocitrate dehydrogenase from Escherichia coli."
    Lee M.E., Dyer D.H., Klein O.D., Bolduc J.M., Stoddard B.L., Koshland D.E. Jr.
    Biochemistry 34:378-384(1995) [PubMed] [Europe PMC] [Abstract]
    Cited for: ENZYME KINETICS, MUTAGENESIS OF TYR-160 AND LYS-230.
  8. "Escherichia coli proteome analysis using the gene-protein database."
    VanBogelen R.A., Abshire K.Z., Moldover B., Olson E.R., Neidhardt F.C.
    Electrophoresis 18:1243-1251(1997) [PubMed] [Europe PMC] [Abstract]
    Cited for: IDENTIFICATION BY 2D-GEL.
  9. "Lysine acetylation is a highly abundant and evolutionarily conserved modification in Escherichia coli."
    Zhang J., Sprung R., Pei J., Tan X., Kim S., Zhu H., Liu C.F., Grishin N.V., Zhao Y.
    Mol. Cell. Proteomics 8:215-225(2009) [PubMed] [Europe PMC] [Abstract]
    Cited for: ACETYLATION [LARGE SCALE ANALYSIS] AT LYS-142, IDENTIFICATION BY MASS SPECTROMETRY.
    Strain: K12 / JW1106 and K12 / MG1655 / ATCC 47076.
  10. "Identification of lysine succinylation as a new post-translational modification."
    Zhang Z., Tan M., Xie Z., Dai L., Chen Y., Zhao Y.
    Nat. Chem. Biol. 7:58-63(2011) [PubMed] [Europe PMC] [Abstract]
    Cited for: CATALYTIC ACTIVITY, SUCCINYLATION AT LYS-100 AND LYS-242, MUTAGENESIS OF LYS-100 AND LYS-242.
    Strain: K12.
  11. "Regulation of an enzyme by phosphorylation at the active site."
    Hurley J.H., Dean A.M., Sohl J.L., Koshland D.E. Jr., Stroud R.M.
    Science 249:1012-1016(1990) [PubMed] [Europe PMC] [Abstract]
    Cited for: X-RAY CRYSTALLOGRAPHY (2.5 ANGSTROMS) IN COMPLEX WITH ISOCITRATE AND MAGNESIUM, PHOSPHORYLATION AT SER-113, MUTAGENESIS OF SER-113.
  12. "Mutagenesis and Laue structures of enzyme intermediates: isocitrate dehydrogenase."
    Bolduc J.M., Dyer D.H., Scott W.G., Singer P., Sweet R.M., Koshland D.E. Jr., Stoddard B.L.
    Science 268:1312-1318(1995) [PubMed] [Europe PMC] [Abstract]
    Cited for: X-RAY CRYSTALLOGRAPHY (2.5 ANGSTROMS) IN COMPLEX WITH ISOCITRATE; NADP AND MAGNESIUM, MUTAGENESIS OF TYR-160 AND LYS-230, BIOPHYSICOCHEMICAL PROPERTIES.
  13. "Structure of a bacterial enzyme regulated by phosphorylation, isocitrate dehydrogenase."
    Hurley J.H., Thorsness P.E., Ramalingam V., Helmers N.H., Koshland D.E. Jr., Stroud R.M.
    Proc. Natl. Acad. Sci. U.S.A. 86:8635-8639(1989) [PubMed] [Europe PMC] [Abstract]
    Cited for: X-RAY CRYSTALLOGRAPHY (2.5 ANGSTROMS) IN COMPLEX WITH NADP, SUBUNIT.
  14. "Active site water molecules revealed in the 2.1 A resolution structure of a site-directed mutant of isocitrate dehydrogenase."
    Cherbavaz D.B., Lee M.E., Stroud R.M., Koshland D.E. Jr.
    J. Mol. Biol. 295:377-385(2000) [PubMed] [Europe PMC] [Abstract]
    Cited for: X-RAY CRYSTALLOGRAPHY (2.1 ANGSTROMS) OF MUTANT MET-230.
  15. "Structural basis for a change in substrate specificity: crystal structure of S113E isocitrate dehydrogenase in a complex with isopropylmalate, Mg2+, and NADP."
    Doyle S.A., Beernink P.T., Koshland D.E. Jr.
    Biochemistry 40:4234-4241(2001) [PubMed] [Europe PMC] [Abstract]
    Cited for: X-RAY CRYSTALLOGRAPHY (2.0 ANGSTROMS) OF MUTANT GLU-113 IN COMPLEX WITH SUBSTRATE ANALOG; MAGNESIUM AND NADP.

Entry informationi

Entry nameiIDH_ECOLI
AccessioniPrimary (citable) accession number: P08200
Entry historyi
Integrated into UniProtKB/Swiss-Prot: August 1, 1988
Last sequence update: August 1, 1988
Last modified: March 4, 2015
This is version 148 of the entry and version 1 of the sequence. [Complete history]
Entry statusiReviewed (UniProtKB/Swiss-Prot)
Annotation programProkaryotic Protein Annotation Program

Miscellaneousi

Keywords - Technical termi

3D-structure, Complete proteome, Direct protein sequencing, Reference proteome

Documents

  1. Escherichia coli
    Escherichia coli (strain K12): entries and cross-references to EcoGene
  2. PDB cross-references
    Index of Protein Data Bank (PDB) cross-references
  3. SIMILARITY comments
    Index of protein domains and families

External Data

Dasty 3

Similar proteinsi

Links to similar proteins from the UniProt Reference Clusters (UniRef) at 100%, 90% and 50% sequence identity:
100%UniRef100 combines identical sequences and sub-fragments with 11 or more residues from any organism into Uniref entry.
90%UniRef90 is built by clustering UniRef100 sequences that have at least 90% sequence identity to, and 80% overlap with, the longest sequence (a.k.a seed sequence).
50%UniRef50 is built by clustering UniRef90 seed sequences that have at least 50% sequence identity to, and 80% overlap with, the longest sequence in the cluster.