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Protein

Dihydroorotate dehydrogenase (quinone), mitochondrial

Gene

DHODH

Organism
Homo sapiens (Human)
Status
Reviewed-Annotation score: Annotation score: 5 out of 5-Experimental evidence at protein leveli

Functioni

Catalyzes the conversion of dihydroorotate to orotate with quinone as electron acceptor.

Catalytic activityi

(S)-dihydroorotate + a quinone = orotate + a quinol.1 Publication

Cofactori

FMN1 PublicationNote: Binds 1 FMN per subunit.1 Publication

Pathwayi: UMP biosynthesis via de novo pathway

This protein is involved in step 1 of the subpathway that synthesizes orotate from (S)-dihydroorotate (quinone route).
Proteins known to be involved in this subpathway in this organism are:
  1. Dihydroorotate dehydrogenase (quinone), mitochondrial (DHODH), Dihydroorotate dehydrogenase (quinone), mitochondrial (DHODH)
This subpathway is part of the pathway UMP biosynthesis via de novo pathway, which is itself part of Pyrimidine metabolism.
View all proteins of this organism that are known to be involved in the subpathway that synthesizes orotate from (S)-dihydroorotate (quinone route), the pathway UMP biosynthesis via de novo pathway and in Pyrimidine metabolism.

Sites

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Binding sitei99Substrate1
Binding sitei119FMN2 Publications1
Binding sitei180FMN2 Publications1
Binding sitei211FMN2 Publications1
Active sitei214Nucleophile1
Binding sitei254FMN2 Publications1
Binding sitei282FMN; via carbonyl oxygen2 Publications1
Binding sitei305FMN; via amide nitrogen2 Publications1
Binding sitei334FMN; via amide nitrogen2 Publications1

Regions

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Nucleotide bindingi95 – 99FMN2 Publications5
Nucleotide bindingi355 – 356FMN2 Publications2

GO - Molecular functioni

GO - Biological processi

Complete GO annotation...

Keywords - Molecular functioni

Oxidoreductase

Keywords - Biological processi

Pyrimidine biosynthesis

Keywords - Ligandi

Flavoprotein, FMN

Enzyme and pathway databases

BioCyciZFISH:HS02434-MONOMER.
BRENDAi1.3.5.2. 2681.
1.3.98.1. 2681.
ReactomeiR-HSA-500753. Pyrimidine biosynthesis.
SABIO-RKQ02127.
UniPathwayiUPA00070; UER00946.

Names & Taxonomyi

Protein namesi
Recommended name:
Dihydroorotate dehydrogenase (quinone), mitochondrial (EC:1.3.5.2)
Short name:
DHOdehase
Alternative name(s):
Dihydroorotate oxidase
Gene namesi
Name:DHODH
OrganismiHomo sapiens (Human)
Taxonomic identifieri9606 [NCBI]
Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresPrimatesHaplorrhiniCatarrhiniHominidaeHomo
Proteomesi
  • UP000005640 Componenti: Chromosome 16

Organism-specific databases

HGNCiHGNC:2867. DHODH.

Subcellular locationi

Topology

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Topological domaini1 – 10Mitochondrial matrixBy similarity10
Transmembranei11 – 30HelicalBy similarityAdd BLAST20
Topological domaini31 – 395Mitochondrial intermembraneBy similarityAdd BLAST365

GO - Cellular componenti

Complete GO annotation...

Keywords - Cellular componenti

Membrane, Mitochondrion, Mitochondrion inner membrane

Pathology & Biotechi

Involvement in diseasei

Postaxial acrofacial dysostosis (POADS)1 Publication
The disease is caused by mutations affecting the gene represented in this entry.
Disease descriptionPOADS is characterized by severe micrognathia, cleft lip and/or palate, hypoplasia or aplasia of the posterior elements of the limbs, coloboma of the eyelids and supernumerary nipples. POADS is a very rare disorder: only 2 multiplex families, each consisting of 2 affected siblings born to unaffected, nonconsanguineous parents, have been described among a total of around 30 reported cases.
See also OMIM:263750
Feature keyPosition(s)DescriptionActionsGraphical viewLength
Natural variantiVAR_06241219G → E in POADS. 1 PublicationCorresponds to variant rs267606765dbSNPEnsembl.1
Natural variantiVAR_062413135R → C in POADS. 1 PublicationCorresponds to variant rs201230446dbSNPEnsembl.1
Natural variantiVAR_062414152G → R in POADS. 1 PublicationCorresponds to variant rs267606766dbSNPEnsembl.1
Natural variantiVAR_062415199R → C in POADS. 1 PublicationCorresponds to variant rs267606769dbSNPEnsembl.1
Natural variantiVAR_062416202G → A in POADS. 1 PublicationCorresponds to variant rs267606767dbSNPEnsembl.1
Natural variantiVAR_062417202G → D in POADS. 1 PublicationCorresponds to variant rs267606767dbSNPEnsembl.1
Natural variantiVAR_062418244R → W in POADS. 1 PublicationCorresponds to variant rs267606768dbSNPEnsembl.1
Natural variantiVAR_062419284T → I in POADS. 1 Publication1
Natural variantiVAR_062420346R → W in POADS. 1 PublicationCorresponds to variant rs201947120dbSNPEnsembl.1
Natural variantiVAR_062421392D → G in POADS. 1 PublicationCorresponds to variant rs779076692dbSNPEnsembl.1

Keywords - Diseasei

Disease mutation

Organism-specific databases

DisGeNETi1723.
MalaCardsiDHODH.
MIMi263750. phenotype.
OpenTargetsiENSG00000102967.
Orphaneti246. Postaxial acrofacial dysostosis.
PharmGKBiPA27327.

Chemistry databases

ChEMBLiCHEMBL1966.
DrugBankiDB01117. Atovaquone.
DB01097. Leflunomide.
DB08880. Teriflunomide.
GuidetoPHARMACOLOGYi2604.

Polymorphism and mutation databases

BioMutaiDHODH.
DMDMi56405372.

PTM / Processingi

Molecule processing

Feature keyPosition(s)DescriptionActionsGraphical viewLength
ChainiPRO_00000298841 – 395Dihydroorotate dehydrogenase (quinone), mitochondrialAdd BLAST395
Transit peptidei1 – 10Mitochondrion; not cleavedBy similarity10

Post-translational modificationi

The uncleaved transit peptide is required for mitochondrial targeting and proper membrane integration.

Proteomic databases

EPDiQ02127.
MaxQBiQ02127.
PaxDbiQ02127.
PeptideAtlasiQ02127.
PRIDEiQ02127.
TopDownProteomicsiQ02127.

PTM databases

iPTMnetiQ02127.
PhosphoSitePlusiQ02127.

Expressioni

Gene expression databases

BgeeiENSG00000102967.
CleanExiHS_DHODH.
ExpressionAtlasiQ02127. baseline and differential.
GenevisibleiQ02127. HS.

Organism-specific databases

HPAiHPA010123.
HPA011942.

Interactioni

Subunit structurei

Monomer.2 Publications

Protein-protein interaction databases

BioGridi108068. 13 interactors.
IntActiQ02127. 2 interactors.
STRINGi9606.ENSP00000219240.

Chemistry databases

BindingDBiQ02127.

Structurei

Secondary structure

1395
Legend: HelixTurnBeta strandPDB Structure known for this area
Show more details
Feature keyPosition(s)DescriptionActionsGraphical viewLength
Helixi34 – 39Combined sources6
Helixi41 – 48Combined sources8
Helixi51 – 63Combined sources13
Helixi76 – 78Combined sources3
Beta strandi80 – 82Combined sources3
Beta strandi85 – 93Combined sources9
Turni95 – 100Combined sources6
Beta strandi101 – 103Combined sources3
Helixi104 – 109Combined sources6
Beta strandi113 – 120Combined sources8
Beta strandi133 – 136Combined sources4
Helixi137 – 139Combined sources3
Beta strandi141 – 144Combined sources4
Helixi153 – 161Combined sources9
Helixi164 – 172Combined sources9
Beta strandi177 – 181Combined sources5
Helixi190 – 201Combined sources12
Helixi202 – 204Combined sources3
Beta strandi206 – 212Combined sources7
Helixi220 – 224Combined sources5
Helixi226 – 241Combined sources16
Helixi245 – 247Combined sources3
Beta strandi250 – 255Combined sources6
Helixi261 – 274Combined sources14
Beta strandi278 – 281Combined sources4
Turni295 – 298Combined sources4
Beta strandi299 – 305Combined sources7
Helixi306 – 308Combined sources3
Helixi309 – 322Combined sources14
Turni323 – 325Combined sources3
Beta strandi329 – 334Combined sources6
Helixi338 – 347Combined sources10
Beta strandi349 – 355Combined sources7
Helixi356 – 361Combined sources6
Helixi364 – 379Combined sources16
Helixi385 – 388Combined sources4
Helixi391 – 393Combined sources3

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
PDB entryMethodResolution (Å)ChainPositionsPDBsum
1D3GX-ray1.60A29-395[»]
1D3HX-ray1.80A29-395[»]
2B0MX-ray2.00A29-395[»]
2BXVX-ray2.15A29-395[»]
2FPTX-ray2.40A29-395[»]
2FPVX-ray1.80A29-395[»]
2FPYX-ray2.00A29-395[»]
2FQIX-ray1.95A29-395[»]
2PRHX-ray2.40A29-395[»]
2PRLX-ray2.10A29-395[»]
2PRMX-ray3.00A29-395[»]
2WV8X-ray1.90A31-395[»]
3F1QX-ray2.00A29-395[»]
3FJ6X-ray1.80A29-395[»]
3FJLX-ray1.90A29-395[»]
3G0UX-ray2.00A29-395[»]
3G0XX-ray1.80A29-395[»]
3KVJX-ray1.94A29-395[»]
3KVKX-ray2.05A29-395[»]
3KVLX-ray1.85A29-395[»]
3KVMX-ray2.00A29-395[»]
3U2OX-ray2.18A1-395[»]
3W7RX-ray1.68A29-395[»]
3ZWSX-ray1.60A29-395[»]
3ZWTX-ray1.55A29-395[»]
4IGHX-ray1.30A32-395[»]
4JGDX-ray2.05A29-395[»]
4JS3X-ray2.00A29-395[»]
4JTSX-ray2.21A29-395[»]
4JTTX-ray2.10A29-395[»]
4JTUX-ray1.90A29-395[»]
4LS0X-ray2.07A29-395[»]
4LS1X-ray2.20A29-395[»]
4LS2X-ray2.27A29-395[»]
4OQVX-ray1.23A32-395[»]
4RK8X-ray2.22A29-395[»]
4RKAX-ray2.71A29-395[»]
4RLIX-ray2.50A29-395[»]
4RR4X-ray2.38A29-395[»]
4YLWX-ray1.79A29-395[»]
4ZL1X-ray1.86A29-395[»]
4ZMGX-ray1.90A29-395[»]
5HINX-ray1.60A29-395[»]
5HQEX-ray1.62A29-395[»]
5K9CX-ray1.66A29-395[»]
5K9DX-ray1.70A29-395[»]
ProteinModelPortaliQ02127.
SMRiQ02127.
ModBaseiSearch...
MobiDBiSearch...

Miscellaneous databases

EvolutionaryTraceiQ02127.

Family & Domainsi

Region

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Regioni144 – 148Substrate binding5
Regioni211 – 216Substrate binding6
Regioni283 – 284Substrate binding2

Sequence similaritiesi

Keywords - Domaini

Transit peptide, Transmembrane, Transmembrane helix

Phylogenomic databases

eggNOGiKOG1436. Eukaryota.
COG0167. LUCA.
GeneTreeiENSGT00500000044924.
HOGENOMiHOG000225103.
HOVERGENiHBG006898.
InParanoidiQ02127.
KOiK00254.
OMAiERIKMGA.
OrthoDBiEOG091G07JK.
PhylomeDBiQ02127.
TreeFamiTF105973.

Family and domain databases

CDDicd04738. DHOD_2_like. 1 hit.
Gene3Di3.20.20.70. 1 hit.
InterProiIPR013785. Aldolase_TIM.
IPR005720. Dihydroorotate_DH.
IPR005719. Dihydroorotate_DH_2.
IPR001295. Dihydroorotate_DH_CS.
[Graphical view]
PfamiPF01180. DHO_dh. 1 hit.
[Graphical view]
TIGRFAMsiTIGR01036. pyrD_sub2. 1 hit.
PROSITEiPS00911. DHODEHASE_1. 1 hit.
PS00912. DHODEHASE_2. 1 hit.
[Graphical view]

Sequencei

Sequence statusi: Complete.

Sequence processingi: The displayed sequence is further processed into a mature form.

Q02127-1 [UniParc]FASTAAdd to basket

« Hide

        10         20         30         40         50
MAWRHLKKRA QDAVIILGGG GLLFASYLMA TGDERFYAEH LMPTLQGLLD
60 70 80 90 100
PESAHRLAVR FTSLGLLPRA RFQDSDMLEV RVLGHKFRNP VGIAAGFDKH
110 120 130 140 150
GEAVDGLYKM GFGFVEIGSV TPKPQEGNPR PRVFRLPEDQ AVINRYGFNS
160 170 180 190 200
HGLSVVEHRL RARQQKQAKL TEDGLPLGVN LGKNKTSVDA AEDYAEGVRV
210 220 230 240 250
LGPLADYLVV NVSSPNTAGL RSLQGKAELR RLLTKVLQER DGLRRVHRPA
260 270 280 290 300
VLVKIAPDLT SQDKEDIASV VKELGIDGLI VTNTTVSRPA GLQGALRSET
310 320 330 340 350
GGLSGKPLRD LSTQTIREMY ALTQGRVPII GVGGVSSGQD ALEKIRAGAS
360 370 380 390
LVQLYTALTF WGPPVVGKVK RELEALLKEQ GFGGVTDAIG ADHRR
Length:395
Mass (Da):42,867
Last modified:December 7, 2004 - v3
Checksum:i072C3169E78C6440
GO

Experimental Info

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Sequence conflicti1 – 2MA → KLP in AAA50163 (PubMed:1446837).Curated2

Natural variant

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Natural variantiVAR_0220947K → Q.2 PublicationsCorresponds to variant rs3213422dbSNPEnsembl.1
Natural variantiVAR_06241219G → E in POADS. 1 PublicationCorresponds to variant rs267606765dbSNPEnsembl.1
Natural variantiVAR_062413135R → C in POADS. 1 PublicationCorresponds to variant rs201230446dbSNPEnsembl.1
Natural variantiVAR_062414152G → R in POADS. 1 PublicationCorresponds to variant rs267606766dbSNPEnsembl.1
Natural variantiVAR_062415199R → C in POADS. 1 PublicationCorresponds to variant rs267606769dbSNPEnsembl.1
Natural variantiVAR_062416202G → A in POADS. 1 PublicationCorresponds to variant rs267606767dbSNPEnsembl.1
Natural variantiVAR_062417202G → D in POADS. 1 PublicationCorresponds to variant rs267606767dbSNPEnsembl.1
Natural variantiVAR_062418244R → W in POADS. 1 PublicationCorresponds to variant rs267606768dbSNPEnsembl.1
Natural variantiVAR_062419284T → I in POADS. 1 Publication1
Natural variantiVAR_062420346R → W in POADS. 1 PublicationCorresponds to variant rs201947120dbSNPEnsembl.1
Natural variantiVAR_062421392D → G in POADS. 1 PublicationCorresponds to variant rs779076692dbSNPEnsembl.1

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
M94065 mRNA. Translation: AAA50163.1.
AK292293 mRNA. Translation: BAF84982.1.
BC065245 mRNA. Translation: AAH65245.1.
CCDSiCCDS42192.1.
PIRiPC1219.
RefSeqiNP_001352.2. NM_001361.4.
UniGeneiHs.654427.

Genome annotation databases

EnsembliENST00000219240; ENSP00000219240; ENSG00000102967.
GeneIDi1723.
KEGGihsa:1723.
UCSCiuc002fbp.4. human.

Keywords - Coding sequence diversityi

Polymorphism

Cross-referencesi

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
M94065 mRNA. Translation: AAA50163.1.
AK292293 mRNA. Translation: BAF84982.1.
BC065245 mRNA. Translation: AAH65245.1.
CCDSiCCDS42192.1.
PIRiPC1219.
RefSeqiNP_001352.2. NM_001361.4.
UniGeneiHs.654427.

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
PDB entryMethodResolution (Å)ChainPositionsPDBsum
1D3GX-ray1.60A29-395[»]
1D3HX-ray1.80A29-395[»]
2B0MX-ray2.00A29-395[»]
2BXVX-ray2.15A29-395[»]
2FPTX-ray2.40A29-395[»]
2FPVX-ray1.80A29-395[»]
2FPYX-ray2.00A29-395[»]
2FQIX-ray1.95A29-395[»]
2PRHX-ray2.40A29-395[»]
2PRLX-ray2.10A29-395[»]
2PRMX-ray3.00A29-395[»]
2WV8X-ray1.90A31-395[»]
3F1QX-ray2.00A29-395[»]
3FJ6X-ray1.80A29-395[»]
3FJLX-ray1.90A29-395[»]
3G0UX-ray2.00A29-395[»]
3G0XX-ray1.80A29-395[»]
3KVJX-ray1.94A29-395[»]
3KVKX-ray2.05A29-395[»]
3KVLX-ray1.85A29-395[»]
3KVMX-ray2.00A29-395[»]
3U2OX-ray2.18A1-395[»]
3W7RX-ray1.68A29-395[»]
3ZWSX-ray1.60A29-395[»]
3ZWTX-ray1.55A29-395[»]
4IGHX-ray1.30A32-395[»]
4JGDX-ray2.05A29-395[»]
4JS3X-ray2.00A29-395[»]
4JTSX-ray2.21A29-395[»]
4JTTX-ray2.10A29-395[»]
4JTUX-ray1.90A29-395[»]
4LS0X-ray2.07A29-395[»]
4LS1X-ray2.20A29-395[»]
4LS2X-ray2.27A29-395[»]
4OQVX-ray1.23A32-395[»]
4RK8X-ray2.22A29-395[»]
4RKAX-ray2.71A29-395[»]
4RLIX-ray2.50A29-395[»]
4RR4X-ray2.38A29-395[»]
4YLWX-ray1.79A29-395[»]
4ZL1X-ray1.86A29-395[»]
4ZMGX-ray1.90A29-395[»]
5HINX-ray1.60A29-395[»]
5HQEX-ray1.62A29-395[»]
5K9CX-ray1.66A29-395[»]
5K9DX-ray1.70A29-395[»]
ProteinModelPortaliQ02127.
SMRiQ02127.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

BioGridi108068. 13 interactors.
IntActiQ02127. 2 interactors.
STRINGi9606.ENSP00000219240.

Chemistry databases

BindingDBiQ02127.
ChEMBLiCHEMBL1966.
DrugBankiDB01117. Atovaquone.
DB01097. Leflunomide.
DB08880. Teriflunomide.
GuidetoPHARMACOLOGYi2604.

PTM databases

iPTMnetiQ02127.
PhosphoSitePlusiQ02127.

Polymorphism and mutation databases

BioMutaiDHODH.
DMDMi56405372.

Proteomic databases

EPDiQ02127.
MaxQBiQ02127.
PaxDbiQ02127.
PeptideAtlasiQ02127.
PRIDEiQ02127.
TopDownProteomicsiQ02127.

Protocols and materials databases

Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsembliENST00000219240; ENSP00000219240; ENSG00000102967.
GeneIDi1723.
KEGGihsa:1723.
UCSCiuc002fbp.4. human.

Organism-specific databases

CTDi1723.
DisGeNETi1723.
GeneCardsiDHODH.
HGNCiHGNC:2867. DHODH.
HPAiHPA010123.
HPA011942.
MalaCardsiDHODH.
MIMi126064. gene.
263750. phenotype.
neXtProtiNX_Q02127.
OpenTargetsiENSG00000102967.
Orphaneti246. Postaxial acrofacial dysostosis.
PharmGKBiPA27327.
GenAtlasiSearch...

Phylogenomic databases

eggNOGiKOG1436. Eukaryota.
COG0167. LUCA.
GeneTreeiENSGT00500000044924.
HOGENOMiHOG000225103.
HOVERGENiHBG006898.
InParanoidiQ02127.
KOiK00254.
OMAiERIKMGA.
OrthoDBiEOG091G07JK.
PhylomeDBiQ02127.
TreeFamiTF105973.

Enzyme and pathway databases

UniPathwayiUPA00070; UER00946.
BioCyciZFISH:HS02434-MONOMER.
BRENDAi1.3.5.2. 2681.
1.3.98.1. 2681.
ReactomeiR-HSA-500753. Pyrimidine biosynthesis.
SABIO-RKQ02127.

Miscellaneous databases

ChiTaRSiDHODH. human.
EvolutionaryTraceiQ02127.
GenomeRNAii1723.
PROiQ02127.
SOURCEiSearch...

Gene expression databases

BgeeiENSG00000102967.
CleanExiHS_DHODH.
ExpressionAtlasiQ02127. baseline and differential.
GenevisibleiQ02127. HS.

Family and domain databases

CDDicd04738. DHOD_2_like. 1 hit.
Gene3Di3.20.20.70. 1 hit.
InterProiIPR013785. Aldolase_TIM.
IPR005720. Dihydroorotate_DH.
IPR005719. Dihydroorotate_DH_2.
IPR001295. Dihydroorotate_DH_CS.
[Graphical view]
PfamiPF01180. DHO_dh. 1 hit.
[Graphical view]
TIGRFAMsiTIGR01036. pyrD_sub2. 1 hit.
PROSITEiPS00911. DHODEHASE_1. 1 hit.
PS00912. DHODEHASE_2. 1 hit.
[Graphical view]
ProtoNetiSearch...

Entry informationi

Entry nameiPYRD_HUMAN
AccessioniPrimary (citable) accession number: Q02127
Secondary accession number(s): A8K8C8, Q6P176
Entry historyi
Integrated into UniProtKB/Swiss-Prot: July 1, 1993
Last sequence update: December 7, 2004
Last modified: November 30, 2016
This is version 176 of the entry and version 3 of the sequence. [Complete history]
Entry statusiReviewed (UniProtKB/Swiss-Prot)
Annotation programChordata Protein Annotation Program
DisclaimerAny medical or genetic information present in this entry is provided for research, educational and informational purposes only. It is not in any way intended to be used as a substitute for professional medical advice, diagnosis, treatment or care.

Miscellaneousi

Miscellaneous

The identification of DHODH defects as the cause of postaxial acrofacial dysostosis (POADS) was obtained via exome sequencing (PubMed:19915526), demonstrating that this method is a powerful tool for identifying genes underlying rare Mendelian disorders. Exome sequencing consists of targeted resequencing of all protein-coding subsequences, which requires around 5% as much sequencing as a whole human genome.1 Publication

Keywords - Technical termi

3D-structure, Complete proteome, Reference proteome

Documents

  1. Human chromosome 16
    Human chromosome 16: entries, gene names and cross-references to MIM
  2. Human entries with polymorphisms or disease mutations
    List of human entries with polymorphisms or disease mutations
  3. Human polymorphisms and disease mutations
    Index of human polymorphisms and disease mutations
  4. MIM cross-references
    Online Mendelian Inheritance in Man (MIM) cross-references in UniProtKB/Swiss-Prot
  5. PATHWAY comments
    Index of metabolic and biosynthesis pathways
  6. PDB cross-references
    Index of Protein Data Bank (PDB) cross-references
  7. SIMILARITY comments
    Index of protein domains and families

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 one 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.