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Protein

Bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase 1

Gene

PAPSS1

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

Functioni

Bifunctional enzyme with both ATP sulfurylase and APS kinase activity, which mediates two steps in the sulfate activation pathway. The first step is the transfer of a sulfate group to ATP to yield adenosine 5'-phosphosulfate (APS), and the second step is the transfer of a phosphate group from ATP to APS yielding 3'-phosphoadenylylsulfate (PAPS: activated sulfate donor used by sulfotransferase). In mammals, PAPS is the sole source of sulfate; APS appears to be only an intermediate in the sulfate-activation pathway. Also involved in the biosynthesis of sulfated L-selectin ligands in endothelial cells.

Catalytic activityi

ATP + sulfate = diphosphate + adenylyl sulfate.
ATP + adenylyl sulfate = ADP + 3'-phosphoadenylyl sulfate.

Enzyme regulationi

Inhibited by chlorate.

Pathwayi: sulfate assimilation

This protein is involved in the pathway sulfate assimilation, which is part of Sulfur metabolism.
View all proteins of this organism that are known to be involved in the pathway sulfate assimilation and in Sulfur metabolism.

Sites

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Active sitei133 – 1331Phosphoserine intermediateBy similarity

Regions

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Nucleotide bindingi59 – 668ATPSequence analysis

GO - Molecular functioni

GO - Biological processi

Complete GO annotation...

Keywords - Molecular functioni

Kinase, Nucleotidyltransferase, Transferase

Keywords - Ligandi

ATP-binding, Nucleotide-binding

Enzyme and pathway databases

BioCyciMetaCyc:HS06566-MONOMER.
BRENDAi2.7.1.25. 2681.
2.7.7.4. 2681.
ReactomeiR-HSA-174362. Transport and synthesis of PAPS.
R-HSA-2408550. Metabolism of ingested H2SeO4 and H2SeO3 into H2Se.
SABIO-RKO43252.
UniPathwayiUPA00097.

Names & Taxonomyi

Protein namesi
Recommended name:
Bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase 1
Short name:
PAPS synthase 1
Short name:
PAPSS 1
Alternative name(s):
Sulfurylase kinase 1
Short name:
SK 1
Short name:
SK1
Including the following 2 domains:
Sulfate adenylyltransferase (EC:2.7.7.4)
Alternative name(s):
ATP-sulfurylase
Sulfate adenylate transferase
Short name:
SAT
Adenylyl-sulfate kinase (EC:2.7.1.25)
Alternative name(s):
3'-phosphoadenosine-5'-phosphosulfate synthase
APS kinase
Adenosine-5'-phosphosulfate 3'-phosphotransferase
Adenylylsulfate 3'-phosphotransferase
Gene namesi
Name:PAPSS1
Synonyms:ATPSK1, PAPSS
OrganismiHomo sapiens (Human)
Taxonomic identifieri9606 [NCBI]
Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresPrimatesHaplorrhiniCatarrhiniHominidaeHomo
Proteomesi
  • UP000005640 Componenti: Chromosome 4

Organism-specific databases

HGNCiHGNC:8603. PAPSS1.

Subcellular locationi

GO - Cellular componenti

Complete GO annotation...

Pathology & Biotechi

Mutagenesis

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Mutagenesisi425 – 4251H → A: Loss of activity. 1 Publication
Mutagenesisi426 – 4261N → K: Increased activity. 1 Publication
Mutagenesisi427 – 4282GH → AA: Loss of activity.
Mutagenesisi427 – 4271G → A: 30% decrease in activity. 1 Publication
Mutagenesisi428 – 4281H → A: Loss of activity. 1 Publication

Organism-specific databases

PharmGKBiPA384.

Polymorphism and mutation databases

BioMutaiPAPSS1.

PTM / Processingi

Molecule processing

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Chaini1 – 624624Bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase 1PRO_0000105959Add
BLAST

Amino acid modifications

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Modified residuei1 – 11N-acetylmethionineCombined sources
Modified residuei12 – 121N6-acetyllysineBy similarity

Keywords - PTMi

Acetylation

Proteomic databases

EPDiO43252.
PaxDbiO43252.
PeptideAtlasiO43252.
PRIDEiO43252.

PTM databases

iPTMnetiO43252.
PhosphoSiteiO43252.

Expressioni

Tissue specificityi

Expressed in testis, pancreas, kidney, thymus, prostate, ovary, small intestine, colon, leukocytes and liver. Also expressed in high endothelial venules (HEV) cells and in cartilage.

Gene expression databases

BgeeiO43252.
CleanExiHS_PAPSS1.
ExpressionAtlasiO43252. baseline and differential.
GenevisibleiO43252. HS.

Organism-specific databases

HPAiHPA049781.

Interactioni

Protein-protein interaction databases

BioGridi114522. 44 interactions.
IntActiO43252. 12 interactions.
MINTiMINT-1372331.
STRINGi9606.ENSP00000265174.

Structurei

Secondary structure

1
624
Legend: HelixTurnBeta strand
Show more details
Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Helixi37 – 437Combined sources
Beta strandi44 – 496Combined sources
Beta strandi53 – 586Combined sources
Helixi65 – 7814Combined sources
Beta strandi83 – 875Combined sources
Helixi88 – 914Combined sources
Turni92 – 987Combined sources
Helixi103 – 12220Combined sources
Beta strandi126 – 1305Combined sources
Helixi136 – 14813Combined sources
Beta strandi153 – 1597Combined sources
Helixi162 – 1687Combined sources
Helixi173 – 1786Combined sources
Beta strandi181 – 1844Combined sources
Turni186 – 1883Combined sources
Beta strandi199 – 2035Combined sources
Turni204 – 2063Combined sources
Helixi209 – 22214Combined sources
Helixi241 – 2433Combined sources
Helixi244 – 2529Combined sources
Beta strandi256 – 2583Combined sources
Helixi261 – 27111Combined sources
Turni272 – 2776Combined sources
Helixi284 – 29310Combined sources
Beta strandi294 – 2963Combined sources
Beta strandi310 – 3123Combined sources
Helixi314 – 3207Combined sources
Beta strandi324 – 3307Combined sources
Beta strandi333 – 34513Combined sources
Helixi348 – 3569Combined sources
Helixi364 – 3718Combined sources
Beta strandi374 – 38310Combined sources
Helixi394 – 3963Combined sources
Helixi400 – 40910Combined sources
Beta strandi413 – 42210Combined sources
Helixi426 – 44217Combined sources
Beta strandi445 – 45410Combined sources
Helixi465 – 47713Combined sources
Helixi483 – 4853Combined sources
Beta strandi486 – 4883Combined sources
Helixi499 – 51214Combined sources
Beta strandi516 – 5205Combined sources
Turni530 – 5323Combined sources
Beta strandi534 – 5374Combined sources
Helixi541 – 5488Combined sources
Beta strandi556 – 5594Combined sources
Beta strandi563 – 5664Combined sources
Turni567 – 5704Combined sources
Beta strandi571 – 5744Combined sources
Helixi580 – 5823Combined sources
Helixi588 – 5969Combined sources
Helixi608 – 62114Combined sources

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
EntryMethodResolution (Å)ChainPositionsPDBsum
1X6VX-ray1.75A/B1-624[»]
1XJQX-ray2.06A/B1-624[»]
1XNJX-ray1.98A/B1-624[»]
2OFWX-ray2.05A/B/C/D/E/F/G/H24-225[»]
2OFXX-ray1.90A/B25-227[»]
2PEYX-ray1.88A/B51-226[»]
2PEZX-ray1.40A/B51-226[»]
2QJFX-ray2.20A/B220-624[»]
ProteinModelPortaliO43252.
SMRiO43252. Positions 25-623.
ModBaseiSearch...
MobiDBiSearch...

Miscellaneous databases

EvolutionaryTraceiO43252.

Family & Domainsi

Region

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Regioni1 – ?220220Adenylyl-sulfate kinaseAdd
BLAST
Regioni?221 – 624404Sulfate adenylyltransferaseAdd
BLAST

Motif

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Motifi521 – 5255PP-motif

Sequence similaritiesi

In the N-terminal section; belongs to the APS kinase family.Curated
In the C-terminal section; belongs to the sulfate adenylyltransferase family.Curated

Phylogenomic databases

eggNOGiKOG0635. Eukaryota.
KOG4238. Eukaryota.
COG0529. LUCA.
COG2046. LUCA.
HOVERGENiHBG053503.
KOiK13811.
OMAiQKTCLQV.
OrthoDBiEOG74TWZ4.
PhylomeDBiO43252.
TreeFamiTF313143.

Family and domain databases

Gene3Di3.40.50.300. 1 hit.
3.40.50.620. 1 hit.
HAMAPiMF_00065. Adenylyl_sulf_kinase.
InterProiIPR002891. APS_kinase.
IPR025980. ATP-Sase_PUA-like_dom.
IPR027417. P-loop_NTPase.
IPR015947. PUA-like_domain.
IPR014729. Rossmann-like_a/b/a_fold.
IPR024951. Sulfurylase_cat_dom.
IPR002650. Sulphate_adenylyltransferase.
[Graphical view]
PfamiPF01747. ATP-sulfurylase. 1 hit.
PF14306. PUA_2. 1 hit.
[Graphical view]
SUPFAMiSSF52540. SSF52540. 1 hit.
SSF88697. SSF88697. 1 hit.
TIGRFAMsiTIGR00455. apsK. 1 hit.
TIGR00339. sopT. 1 hit.

Sequencei

Sequence statusi: Complete.

O43252-1 [UniParc]FASTAAdd to basket

« Hide

        10         20         30         40         50
MEIPGSLCKK VKLSNNAQNW GMQRATNVTY QAHHVSRNKR GQVVGTRGGF
60 70 80 90 100
RGCTVWLTGL SGAGKTTVSM ALEEYLVCHG IPCYTLDGDN IRQGLNKNLG
110 120 130 140 150
FSPEDREENV RRIAEVAKLF ADAGLVCITS FISPYTQDRN NARQIHEGAS
160 170 180 190 200
LPFFEVFVDA PLHVCEQRDV KGLYKKARAG EIKGFTGIDS EYEKPEAPEL
210 220 230 240 250
VLKTDSCDVN DCVQQVVELL QERDIVPVDA SYEVKELYVP ENKLHLAKTD
260 270 280 290 300
AETLPALKIN KVDMQWVQVL AEGWATPLNG FMREREYLQC LHFDCLLDGG
310 320 330 340 350
VINLSVPIVL TATHEDKERL DGCTAFALMY EGRRVAILRN PEFFEHRKEE
360 370 380 390 400
RCARQWGTTC KNHPYIKMVM EQGDWLIGGD LQVLDRVYWN DGLDQYRLTP
410 420 430 440 450
TELKQKFKDM NADAVFAFQL RNPVHNGHAL LMQDTHKQLL ERGYRRPVLL
460 470 480 490 500
LHPLGGWTKD DDVPLMWRMK QHAAVLEEGV LNPETTVVAI FPSPMMYAGP
510 520 530 540 550
TEVQWHCRAR MVAGANFYIV GRDPAGMPHP ETGKDLYEPS HGAKVLTMAP
560 570 580 590 600
GLITLEIVPF RVAAYNKKKK RMDYYDSEHH EDFEFISGTR MRKLAREGQK
610 620
PPEGFMAPKA WTVLTEYYKS LEKA
Length:624
Mass (Da):70,833
Last modified:October 10, 2002 - v2
Checksum:iA3DC9B943E68CDD6
GO

Experimental Info

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Sequence conflicti456 – 4561G → A in CAA71413 (PubMed:9576487).Curated
Sequence conflicti456 – 4561Missing in AAC39894 (PubMed:9668121).Curated
Sequence conflicti519 – 5202IV → MC in AAD09325 (Ref. 4) Curated

Natural variant

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Natural varianti270 – 2701L → F.1 Publication
Corresponds to variant rs1127008 [ dbSNP | Ensembl ].
VAR_014065
Natural varianti587 – 5871S → L.3 Publications
Corresponds to variant rs1127014 [ dbSNP | Ensembl ].
VAR_014064

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
Y10387 mRNA. Translation: CAA71413.1.
U53447 Genomic DNA. Translation: AAC39894.1.
AF033026 mRNA. Translation: AAC28429.1.
AF016496 mRNA. Translation: AAD09325.1.
AF105227 mRNA. Translation: AAF40236.1.
AF097721
, AF097710, AF097711, AF097712, AF097713, AF097714, AF097715, AF097716, AF097717, AF097718, AF097719, AF097720 Genomic DNA. Translation: AAF40235.1.
BC011392 mRNA. Translation: AAH11392.1.
BC050627 mRNA. Translation: AAH50627.1.
CCDSiCCDS3676.1.
PIRiJW0087.
RefSeqiNP_005434.4. NM_005443.4.
XP_011530702.1. XM_011532400.1.
XP_011530703.1. XM_011532401.1.
UniGeneiHs.368610.

Genome annotation databases

EnsembliENST00000265174; ENSP00000265174; ENSG00000138801.
GeneIDi9061.
KEGGihsa:9061.

Keywords - Coding sequence diversityi

Polymorphism

Cross-referencesi

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
Y10387 mRNA. Translation: CAA71413.1.
U53447 Genomic DNA. Translation: AAC39894.1.
AF033026 mRNA. Translation: AAC28429.1.
AF016496 mRNA. Translation: AAD09325.1.
AF105227 mRNA. Translation: AAF40236.1.
AF097721
, AF097710, AF097711, AF097712, AF097713, AF097714, AF097715, AF097716, AF097717, AF097718, AF097719, AF097720 Genomic DNA. Translation: AAF40235.1.
BC011392 mRNA. Translation: AAH11392.1.
BC050627 mRNA. Translation: AAH50627.1.
CCDSiCCDS3676.1.
PIRiJW0087.
RefSeqiNP_005434.4. NM_005443.4.
XP_011530702.1. XM_011532400.1.
XP_011530703.1. XM_011532401.1.
UniGeneiHs.368610.

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
EntryMethodResolution (Å)ChainPositionsPDBsum
1X6VX-ray1.75A/B1-624[»]
1XJQX-ray2.06A/B1-624[»]
1XNJX-ray1.98A/B1-624[»]
2OFWX-ray2.05A/B/C/D/E/F/G/H24-225[»]
2OFXX-ray1.90A/B25-227[»]
2PEYX-ray1.88A/B51-226[»]
2PEZX-ray1.40A/B51-226[»]
2QJFX-ray2.20A/B220-624[»]
ProteinModelPortaliO43252.
SMRiO43252. Positions 25-623.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

BioGridi114522. 44 interactions.
IntActiO43252. 12 interactions.
MINTiMINT-1372331.
STRINGi9606.ENSP00000265174.

PTM databases

iPTMnetiO43252.
PhosphoSiteiO43252.

Polymorphism and mutation databases

BioMutaiPAPSS1.

Proteomic databases

EPDiO43252.
PaxDbiO43252.
PeptideAtlasiO43252.
PRIDEiO43252.

Protocols and materials databases

DNASUi9061.
Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsembliENST00000265174; ENSP00000265174; ENSG00000138801.
GeneIDi9061.
KEGGihsa:9061.

Organism-specific databases

CTDi9061.
GeneCardsiPAPSS1.
HGNCiHGNC:8603. PAPSS1.
HPAiHPA049781.
MIMi603262. gene.
neXtProtiNX_O43252.
PharmGKBiPA384.
GenAtlasiSearch...

Phylogenomic databases

eggNOGiKOG0635. Eukaryota.
KOG4238. Eukaryota.
COG0529. LUCA.
COG2046. LUCA.
HOVERGENiHBG053503.
KOiK13811.
OMAiQKTCLQV.
OrthoDBiEOG74TWZ4.
PhylomeDBiO43252.
TreeFamiTF313143.

Enzyme and pathway databases

UniPathwayiUPA00097.
BioCyciMetaCyc:HS06566-MONOMER.
BRENDAi2.7.1.25. 2681.
2.7.7.4. 2681.
ReactomeiR-HSA-174362. Transport and synthesis of PAPS.
R-HSA-2408550. Metabolism of ingested H2SeO4 and H2SeO3 into H2Se.
SABIO-RKO43252.

Miscellaneous databases

ChiTaRSiPAPSS1. human.
EvolutionaryTraceiO43252.
GeneWikiiPAPSS1.
GenomeRNAii9061.
PROiO43252.
SOURCEiSearch...

Gene expression databases

BgeeiO43252.
CleanExiHS_PAPSS1.
ExpressionAtlasiO43252. baseline and differential.
GenevisibleiO43252. HS.

Family and domain databases

Gene3Di3.40.50.300. 1 hit.
3.40.50.620. 1 hit.
HAMAPiMF_00065. Adenylyl_sulf_kinase.
InterProiIPR002891. APS_kinase.
IPR025980. ATP-Sase_PUA-like_dom.
IPR027417. P-loop_NTPase.
IPR015947. PUA-like_domain.
IPR014729. Rossmann-like_a/b/a_fold.
IPR024951. Sulfurylase_cat_dom.
IPR002650. Sulphate_adenylyltransferase.
[Graphical view]
PfamiPF01747. ATP-sulfurylase. 1 hit.
PF14306. PUA_2. 1 hit.
[Graphical view]
SUPFAMiSSF52540. SSF52540. 1 hit.
SSF88697. SSF88697. 1 hit.
TIGRFAMsiTIGR00455. apsK. 1 hit.
TIGR00339. sopT. 1 hit.
ProtoNetiSearch...

Publicationsi

« Hide 'large scale' publications
  1. "Sulfation in high endothelial venules: cloning and expression of the human PAPS synthetase."
    Girard J.-P., Baekkevold E.S., Amalric F.
    FASEB J. 12:603-612(1998) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA].
    Tissue: Tonsil.
  2. "Molecular cloning, expression, and characterization of human bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase and its functional domains."
    Venkatachalam K.V., Akita H., Strott C.A.
    J. Biol. Chem. 273:19311-19320(1998) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [GENOMIC DNA], VARIANTS PHE-270 AND LEU-587.
    Tissue: Fetal brain.
  3. "cDNA cloning, expression, and characterization of the human bifunctional ATP sulfurylase/adenosine 5'-phosphosulfate kinase enzyme."
    Yanagisawa K., Sakakibara Y., Suiko M., Takami Y., Nakayama T., Nakajima H., Takayanagi K., Natori Y., Liu M.-C.
    Biosci. Biotechnol. Biochem. 62:1037-1040(1998) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA].
    Tissue: Brain.
  4. "Human ATP sulfurylase/APS kinase."
    Deyrup A.T.
    Submitted (JUL-1997) to the EMBL/GenBank/DDBJ databases
    Cited for: NUCLEOTIDE SEQUENCE [MRNA], VARIANT LEU-587.
  5. "Human 3'-phosphoadenosine 5'-phosphosulfate synthetase 1 (PAPSS1) and PAPSS2: gene cloning, characterization and chromosomal localization."
    Xu Z.-H., Otterness D.M., Freimuth R.R., Carlini E.J., Wood T.C., Mitchell S., Moon E., Kim U.-J., Xu J.-P., Siciliano M.J., Weinshilboum R.M.
    Biochem. Biophys. Res. Commun. 268:437-444(2000) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [GENOMIC DNA / MRNA], VARIANT LEU-587.
    Tissue: Brain.
  6. "The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC)."
    The MGC Project Team
    Genome Res. 14:2121-2127(2004) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE MRNA].
    Tissue: Eye and Uterus.
  7. "Site-selected mutagenesis of a conserved nucleotide binding HXGH motif located in the ATP sulfurylase domain of human bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase."
    Venkatachalam K.V., Fuda H., Koonin E.V., Strott C.A.
    J. Biol. Chem. 274:2601-2604(1999) [PubMed] [Europe PMC] [Abstract]
    Cited for: MUTAGENESIS OF HIS-425; ASN-426; GLY-427 AND HIS-428.
  8. Cited for: IDENTIFICATION BY MASS SPECTROMETRY [LARGE SCALE ANALYSIS].
  9. "Comparative large-scale characterisation of plant vs. mammal proteins reveals similar and idiosyncratic N-alpha acetylation features."
    Bienvenut W.V., Sumpton D., Martinez A., Lilla S., Espagne C., Meinnel T., Giglione C.
    Mol. Cell. Proteomics 11:M111.015131-M111.015131(2012) [PubMed] [Europe PMC] [Abstract]
    Cited for: ACETYLATION [LARGE SCALE ANALYSIS] AT MET-1, IDENTIFICATION BY MASS SPECTROMETRY [LARGE SCALE ANALYSIS].

Entry informationi

Entry nameiPAPS1_HUMAN
AccessioniPrimary (citable) accession number: O43252
Secondary accession number(s): O43841
, O75332, Q96FB1, Q96TF4, Q9P1P9, Q9UE98
Entry historyi
Integrated into UniProtKB/Swiss-Prot: May 30, 2000
Last sequence update: October 10, 2002
Last modified: June 8, 2016
This is version 172 of the entry and version 2 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

Keywords - Technical termi

3D-structure, Complete proteome, Multifunctional enzyme, Reference proteome

Documents

  1. Human chromosome 4
    Human chromosome 4: 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.