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Protein

Glutathione synthetase

Gene

GSS

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

Functioni

Catalytic activityi

ATP + gamma-L-glutamyl-L-cysteine + glycine = ADP + phosphate + glutathione.

Cofactori

Mg2+1 PublicationNote: Binds 1 Mg2+ ion per subunit.1 Publication

Pathwayi: glutathione biosynthesis

This protein is involved in step 2 of the subpathway that synthesizes glutathione from L-cysteine and L-glutamate.
Proteins known to be involved in the 2 steps of the subpathway in this organism are:
  1. Glutamate--cysteine ligase regulatory subunit (GCLM), Glutamate--cysteine ligase catalytic subunit (GCLC)
  2. Glutathione synthetase, Glutathione synthetase (GSS), Glutathione synthetase, Glutathione synthetase (HEL-S-64p)
This subpathway is part of the pathway glutathione biosynthesis, which is itself part of Sulfur metabolism.
View all proteins of this organism that are known to be involved in the subpathway that synthesizes glutathione from L-cysteine and L-glutamate, the pathway glutathione biosynthesis and in Sulfur metabolism.

Sites

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Binding sitei125Substrate1
Metal bindingi144Magnesium1
Binding sitei144ATP1
Metal bindingi146Magnesium1
Binding sitei220Substrate1
Binding sitei305ATP1
Metal bindingi368Magnesium1
Binding sitei375ATP1
Binding sitei425ATP1
Binding sitei450Substrate1
Binding sitei452ATP1
Binding sitei458ATP; via carbonyl oxygen1

Regions

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Nucleotide bindingi364 – 373ATP10
Nucleotide bindingi398 – 401ATP4

GO - Molecular functioni

  • ATP binding Source: UniProtKB
  • glutathione binding Source: UniProtKB
  • glutathione synthase activity Source: Reactome
  • glycine binding Source: Ensembl
  • magnesium ion binding Source: UniProtKB
  • protein homodimerization activity Source: UniProtKB

GO - Biological processi

  • aging Source: Ensembl
  • cellular amino acid metabolic process Source: ProtInc
  • glutathione biosynthetic process Source: Reactome
  • nervous system development Source: ProtInc
  • response to amino acid Source: Ensembl
  • response to cadmium ion Source: Ensembl
  • response to nutrient levels Source: Ensembl
  • response to oxidative stress Source: ProtInc
  • response to tumor necrosis factor Source: Ensembl
  • response to xenobiotic stimulus Source: Ensembl
Complete GO annotation...

Keywords - Molecular functioni

Ligase

Keywords - Biological processi

Glutathione biosynthesis

Keywords - Ligandi

ATP-binding, Magnesium, Metal-binding, Nucleotide-binding

Enzyme and pathway databases

BioCyciMetaCyc:HS02174-MONOMER.
ZFISH:ENSG00000180613-MONOMER.
ZFISH:HS02174-MONOMER.
BRENDAi6.3.2.3. 2681.
ReactomeiR-HSA-174403. Glutathione synthesis and recycling.
SABIO-RKP48637.
UniPathwayiUPA00142; UER00210.

Names & Taxonomyi

Protein namesi
Recommended name:
Glutathione synthetase (EC:6.3.2.3)
Short name:
GSH synthetase
Short name:
GSH-S
Alternative name(s):
Glutathione synthase
Gene namesi
Name:GSS
OrganismiHomo sapiens (Human)
Taxonomic identifieri9606 [NCBI]
Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresPrimatesHaplorrhiniCatarrhiniHominidaeHomo
Proteomesi
  • UP000005640 Componenti: Chromosome 20

Organism-specific databases

HGNCiHGNC:4624. GSS.

Subcellular locationi

GO - Cellular componenti

  • cytosol Source: GO_Central
  • extracellular exosome Source: UniProtKB
Complete GO annotation...

Pathology & Biotechi

Involvement in diseasei

Glutathione synthetase deficiency (GSS deficiency)2 Publications
The disease is caused by mutations affecting the gene represented in this entry.
Disease descriptionSevere form characterized by an increased rate of hemolysis and defective function of the central nervous system.
See also OMIM:266130
Feature keyPosition(s)DescriptionActionsGraphical viewLength
Natural variantiVAR_00360226A → D in GSS deficiency. Corresponds to variant rs759253242dbSNPEnsembl.1
Natural variantiVAR_003603188L → P in GSS deficiency; 100-fold reduction of activity. 1
Natural variantiVAR_003604219D → A in GSS deficiency. 1
Natural variantiVAR_003605219D → G in GSS deficiency. 1 PublicationCorresponds to variant rs28938472dbSNPEnsembl.1
Natural variantiVAR_003606254L → R in GSS deficiency. 1
Natural variantiVAR_003607267R → W in GSS deficiency. 1 PublicationCorresponds to variant rs121909308dbSNPEnsembl.1
Natural variantiVAR_003608270Y → C in GSS deficiency; 100-fold reduction of activity. 1
Natural variantiVAR_003609270Y → H in GSS deficiency; 100-fold reduction of activity. 1
Natural variantiVAR_003610283R → C in GSS deficiency; 10-fold reduction of activity. 1 PublicationCorresponds to variant rs121909309dbSNPEnsembl.1
Natural variantiVAR_003611286L → Q in GSS deficiency. 1
Natural variantiVAR_003612330R → C in GSS deficiency. Corresponds to variant rs148640446dbSNPEnsembl.1
Natural variantiVAR_003613464G → V in GSS deficiency. 1
Natural variantiVAR_003614469D → E in GSS deficiency. 1
Glutathione synthetase deficiency of erythrocytes (GLUSYNDE)
The disease is caused by mutations affecting the gene represented in this entry.
Disease descriptionMild form causing hemolytic anemia.
See also OMIM:231900

Keywords - Diseasei

Disease mutation, Hereditary hemolytic anemia

Organism-specific databases

DisGeNETi2937.
MalaCardsiGSS.
MIMi231900. phenotype.
266130. phenotype.
OpenTargetsiENSG00000100983.
Orphaneti289846. Glutathione synthetase deficiency with 5-oxoprolinuria.
289849. Glutathione synthetase deficiency without 5-oxoprolinuria.
PharmGKBiPA29015.

Chemistry databases

DrugBankiDB06151. Acetylcysteine.
DB00143. Glutathione.
DB00145. Glycine.
DB00151. L-Cysteine.

Polymorphism and mutation databases

BioMutaiGSS.
DMDMi1346191.

PTM / Processingi

Molecule processing

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Initiator methionineiRemovedCombined sources
ChainiPRO_00002112602 – 474Glutathione synthetaseAdd BLAST473

Amino acid modifications

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Modified residuei2N-acetylalanineCombined sources1
Modified residuei415PhosphoserineCombined sources1

Keywords - PTMi

Acetylation, Phosphoprotein

Proteomic databases

EPDiP48637.
PaxDbiP48637.
PeptideAtlasiP48637.
PRIDEiP48637.

2D gel databases

OGPiP48637.
REPRODUCTION-2DPAGEIPI00010706.

PTM databases

iPTMnetiP48637.
PhosphoSitePlusiP48637.

Expressioni

Gene expression databases

BgeeiENSG00000100983.
CleanExiHS_GSS.
ExpressionAtlasiP48637. baseline and differential.
GenevisibleiP48637. HS.

Organism-specific databases

HPAiHPA054508.
HPA059315.

Interactioni

Subunit structurei

Homodimer.1 Publication

Binary interactionsi

WithEntry#Exp.IntActNotes
itself4EBI-2969145,EBI-2969145
TERF1P542742EBI-2969145,EBI-710997

GO - Molecular functioni

  • protein homodimerization activity Source: UniProtKB

Protein-protein interaction databases

BioGridi109192. 27 interactors.
IntActiP48637. 3 interactors.
MINTiMINT-5001027.
STRINGi9606.ENSP00000216951.

Structurei

Secondary structure

1474
Legend: HelixTurnBeta strandPDB Structure known for this area
Show more details
Feature keyPosition(s)DescriptionActionsGraphical viewLength
Helixi6 – 9Combined sources4
Helixi12 – 28Combined sources17
Beta strandi32 – 34Combined sources3
Beta strandi43 – 47Combined sources5
Beta strandi50 – 53Combined sources4
Beta strandi56 – 58Combined sources3
Helixi59 – 67Combined sources9
Helixi69 – 81Combined sources13
Helixi83 – 91Combined sources9
Helixi93 – 96Combined sources4
Helixi98 – 113Combined sources16
Beta strandi119 – 132Combined sources14
Beta strandi134 – 136Combined sources3
Beta strandi138 – 146Combined sources9
Helixi153 – 158Combined sources6
Helixi160 – 169Combined sources10
Helixi173 – 176Combined sources4
Helixi184 – 199Combined sources16
Beta strandi205 – 209Combined sources5
Helixi217 – 228Combined sources12
Turni229 – 231Combined sources3
Beta strandi234 – 237Combined sources4
Helixi239 – 245Combined sources7
Beta strandi246 – 248Combined sources3
Beta strandi254 – 256Combined sources3
Beta strandi259 – 268Combined sources10
Helixi272 – 274Combined sources3
Helixi277 – 288Combined sources12
Beta strandi289 – 295Combined sources7
Helixi297 – 301Combined sources5
Helixi305 – 310Combined sources6
Helixi316 – 320Combined sources5
Helixi325 – 333Combined sources9
Beta strandi338 – 340Combined sources3
Beta strandi342 – 344Combined sources3
Helixi345 – 356Combined sources12
Helixi358 – 360Combined sources3
Beta strandi361 – 366Combined sources6
Beta strandi369 – 371Combined sources3
Helixi376 – 386Combined sources11
Helixi390 – 394Combined sources5
Beta strandi395 – 399Combined sources5
Beta strandi406 – 411Combined sources6
Beta strandi418 – 435Combined sources18
Beta strandi438 – 453Combined sources16
Turni461 – 464Combined sources4
Beta strandi467 – 469Combined sources3
Beta strandi472 – 474Combined sources3

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
PDB entryMethodResolution (Å)ChainPositionsPDBsum
2HGSX-ray2.10A1-474[»]
ProteinModelPortaliP48637.
SMRiP48637.
ModBaseiSearch...
MobiDBiSearch...

Miscellaneous databases

EvolutionaryTraceiP48637.

Family & Domainsi

Region

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Regioni148 – 151Substrate binding4
Regioni214 – 216Substrate binding3
Regioni267 – 270Substrate binding4
Regioni461 – 462Substrate binding2

Sequence similaritiesi

Belongs to the eukaryotic GSH synthase family.Curated

Phylogenomic databases

eggNOGiKOG0021. Eukaryota.
ENOG410XPHH. LUCA.
GeneTreeiENSGT00390000013764.
HOGENOMiHOG000172641.
HOVERGENiHBG002458.
InParanoidiP48637.
KOiK01920.
OMAiYMPRQYS.
OrthoDBiEOG091G05V8.
PhylomeDBiP48637.
TreeFamiTF105187.

Family and domain databases

Gene3Di1.10.1080.10. 2 hits.
3.30.1490.50. 1 hit.
3.30.1490.80. 2 hits.
3.40.50.1760. 1 hit.
InterProiIPR004887. Glutathione_synth_subst-bd_euk.
IPR014042. Glutathione_synthase_a-hlx_euk.
IPR014709. Glutathione_synthase_dom.
IPR005615. Glutathione_synthase_euk.
IPR014049. Glutathione_synthase_N_euk.
IPR016185. PreATP-grasp_dom.
[Graphical view]
PANTHERiPTHR11130. PTHR11130. 1 hit.
PfamiPF03917. GSH_synth_ATP. 1 hit.
PF03199. GSH_synthase. 1 hit.
[Graphical view]
PIRSFiPIRSF001558. GSHase. 1 hit.
SUPFAMiSSF52440. SSF52440. 1 hit.
TIGRFAMsiTIGR01986. glut_syn_euk. 1 hit.

Sequences (2)i

Sequence statusi: Complete.

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

This entry describes 2 isoformsi produced by alternative splicing. AlignAdd to basket

Isoform 1 (identifier: P48637-1) [UniParc]FASTAAdd to basket

This isoform has been chosen as the 'canonical' sequence. All positional information in this entry refers to it. This is also the sequence that appears in the downloadable versions of the entry.

« Hide

        10         20         30         40         50
MATNWGSLLQ DKQQLEELAR QAVDRALAEG VLLRTSQEPT SSEVVSYAPF
60 70 80 90 100
TLFPSLVPSA LLEQAYAVQM DFNLLVDAVS QNAAFLEQTL SSTIKQDDFT
110 120 130 140 150
ARLFDIHKQV LKEGIAQTVF LGLNRSDYMF QRSADGSPAL KQIEINTISA
160 170 180 190 200
SFGGLASRTP AVHRHVLSVL SKTKEAGKIL SNNPSKGLAL GIAKAWELYG
210 220 230 240 250
SPNALVLLIA QEKERNIFDQ RAIENELLAR NIHVIRRTFE DISEKGSLDQ
260 270 280 290 300
DRRLFVDGQE IAVVYFRDGY MPRQYSLQNW EARLLLERSH AAKCPDIATQ
310 320 330 340 350
LAGTKKVQQE LSRPGMLEML LPGQPEAVAR LRATFAGLYS LDVGEEGDQA
360 370 380 390 400
IAEALAAPSR FVLKPQREGG GNNLYGEEMV QALKQLKDSE ERASYILMEK
410 420 430 440 450
IEPEPFENCL LRPGSPARVV QCISELGIFG VYVRQEKTLV MNKHVGHLLR
460 470
TKAIEHADGG VAAGVAVLDN PYPV
Length:474
Mass (Da):52,385
Last modified:February 1, 1996 - v1
Checksum:i3C25EF7072EFE058
GO
Isoform 2 (identifier: P48637-2) [UniParc]FASTAAdd to basket

The sequence of this isoform differs from the canonical sequence as follows:
     93-203: Missing.

Note: Detected in colon, kidney, lung, liver, placenta, peripheral blood and uterus, but not in heart, skeletal muscle and spleen.
Show »
Length:363
Mass (Da):40,349
Checksum:i931DA0F137EE1634
GO

Natural variant

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Natural variantiVAR_00360226A → D in GSS deficiency. Corresponds to variant rs759253242dbSNPEnsembl.1
Natural variantiVAR_003603188L → P in GSS deficiency; 100-fold reduction of activity. 1
Natural variantiVAR_003604219D → A in GSS deficiency. 1
Natural variantiVAR_003605219D → G in GSS deficiency. 1 PublicationCorresponds to variant rs28938472dbSNPEnsembl.1
Natural variantiVAR_025047236R → Q.1 PublicationCorresponds to variant rs34239729dbSNPEnsembl.1
Natural variantiVAR_003606254L → R in GSS deficiency. 1
Natural variantiVAR_003607267R → W in GSS deficiency. 1 PublicationCorresponds to variant rs121909308dbSNPEnsembl.1
Natural variantiVAR_003608270Y → C in GSS deficiency; 100-fold reduction of activity. 1
Natural variantiVAR_003609270Y → H in GSS deficiency; 100-fold reduction of activity. 1
Natural variantiVAR_003610283R → C in GSS deficiency; 10-fold reduction of activity. 1 PublicationCorresponds to variant rs121909309dbSNPEnsembl.1
Natural variantiVAR_003611286L → Q in GSS deficiency. 1
Natural variantiVAR_003612330R → C in GSS deficiency. Corresponds to variant rs148640446dbSNPEnsembl.1
Natural variantiVAR_025048437K → E.2 PublicationsCorresponds to variant rs34852238dbSNPEnsembl.1
Natural variantiVAR_003613464G → V in GSS deficiency. 1
Natural variantiVAR_003614469D → E in GSS deficiency. 1

Alternative sequence

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Alternative sequenceiVSP_04761793 – 203Missing in isoform 2. 1 PublicationAdd BLAST111

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
L42531 mRNA. Translation: AAA69492.1.
AB459500 mRNA. Translation: BAG75452.1.
U34683 mRNA. Translation: AAB62390.1.
AK312492 mRNA. Translation: BAG35394.1.
DQ074975 Genomic DNA. Translation: AAY57328.1.
AL133324 Genomic DNA. Translation: CAB93423.1.
CH471077 Genomic DNA. Translation: EAW76239.1.
CH471077 Genomic DNA. Translation: EAW76240.1.
BC007927 mRNA. Translation: AAH07927.1.
CCDSiCCDS13245.1. [P48637-1]
PIRiS56748.
RefSeqiNP_000169.1. NM_000178.3. [P48637-1]
NP_001309423.1. NM_001322494.1. [P48637-1]
NP_001309424.1. NM_001322495.1. [P48637-1]
UniGeneiHs.82327.

Genome annotation databases

EnsembliENST00000216951; ENSP00000216951; ENSG00000100983. [P48637-1]
ENST00000451957; ENSP00000407517; ENSG00000100983. [P48637-2]
GeneIDi2937.
KEGGihsa:2937.
UCSCiuc010zuo.3. human. [P48637-1]

Keywords - Coding sequence diversityi

Alternative splicing, Polymorphism

Cross-referencesi

Web resourcesi

NIEHS-SNPs

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
L42531 mRNA. Translation: AAA69492.1.
AB459500 mRNA. Translation: BAG75452.1.
U34683 mRNA. Translation: AAB62390.1.
AK312492 mRNA. Translation: BAG35394.1.
DQ074975 Genomic DNA. Translation: AAY57328.1.
AL133324 Genomic DNA. Translation: CAB93423.1.
CH471077 Genomic DNA. Translation: EAW76239.1.
CH471077 Genomic DNA. Translation: EAW76240.1.
BC007927 mRNA. Translation: AAH07927.1.
CCDSiCCDS13245.1. [P48637-1]
PIRiS56748.
RefSeqiNP_000169.1. NM_000178.3. [P48637-1]
NP_001309423.1. NM_001322494.1. [P48637-1]
NP_001309424.1. NM_001322495.1. [P48637-1]
UniGeneiHs.82327.

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
PDB entryMethodResolution (Å)ChainPositionsPDBsum
2HGSX-ray2.10A1-474[»]
ProteinModelPortaliP48637.
SMRiP48637.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

BioGridi109192. 27 interactors.
IntActiP48637. 3 interactors.
MINTiMINT-5001027.
STRINGi9606.ENSP00000216951.

Chemistry databases

DrugBankiDB06151. Acetylcysteine.
DB00143. Glutathione.
DB00145. Glycine.
DB00151. L-Cysteine.

PTM databases

iPTMnetiP48637.
PhosphoSitePlusiP48637.

Polymorphism and mutation databases

BioMutaiGSS.
DMDMi1346191.

2D gel databases

OGPiP48637.
REPRODUCTION-2DPAGEIPI00010706.

Proteomic databases

EPDiP48637.
PaxDbiP48637.
PeptideAtlasiP48637.
PRIDEiP48637.

Protocols and materials databases

DNASUi2937.
Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsembliENST00000216951; ENSP00000216951; ENSG00000100983. [P48637-1]
ENST00000451957; ENSP00000407517; ENSG00000100983. [P48637-2]
GeneIDi2937.
KEGGihsa:2937.
UCSCiuc010zuo.3. human. [P48637-1]

Organism-specific databases

CTDi2937.
DisGeNETi2937.
GeneCardsiGSS.
HGNCiHGNC:4624. GSS.
HPAiHPA054508.
HPA059315.
MalaCardsiGSS.
MIMi231900. phenotype.
266130. phenotype.
601002. gene.
neXtProtiNX_P48637.
OpenTargetsiENSG00000100983.
Orphaneti289846. Glutathione synthetase deficiency with 5-oxoprolinuria.
289849. Glutathione synthetase deficiency without 5-oxoprolinuria.
PharmGKBiPA29015.
GenAtlasiSearch...

Phylogenomic databases

eggNOGiKOG0021. Eukaryota.
ENOG410XPHH. LUCA.
GeneTreeiENSGT00390000013764.
HOGENOMiHOG000172641.
HOVERGENiHBG002458.
InParanoidiP48637.
KOiK01920.
OMAiYMPRQYS.
OrthoDBiEOG091G05V8.
PhylomeDBiP48637.
TreeFamiTF105187.

Enzyme and pathway databases

UniPathwayiUPA00142; UER00210.
BioCyciMetaCyc:HS02174-MONOMER.
ZFISH:ENSG00000180613-MONOMER.
ZFISH:HS02174-MONOMER.
BRENDAi6.3.2.3. 2681.
ReactomeiR-HSA-174403. Glutathione synthesis and recycling.
SABIO-RKP48637.

Miscellaneous databases

ChiTaRSiGSS. human.
EvolutionaryTraceiP48637.
GenomeRNAii2937.
PROiP48637.
SOURCEiSearch...

Gene expression databases

BgeeiENSG00000100983.
CleanExiHS_GSS.
ExpressionAtlasiP48637. baseline and differential.
GenevisibleiP48637. HS.

Family and domain databases

Gene3Di1.10.1080.10. 2 hits.
3.30.1490.50. 1 hit.
3.30.1490.80. 2 hits.
3.40.50.1760. 1 hit.
InterProiIPR004887. Glutathione_synth_subst-bd_euk.
IPR014042. Glutathione_synthase_a-hlx_euk.
IPR014709. Glutathione_synthase_dom.
IPR005615. Glutathione_synthase_euk.
IPR014049. Glutathione_synthase_N_euk.
IPR016185. PreATP-grasp_dom.
[Graphical view]
PANTHERiPTHR11130. PTHR11130. 1 hit.
PfamiPF03917. GSH_synth_ATP. 1 hit.
PF03199. GSH_synthase. 1 hit.
[Graphical view]
PIRSFiPIRSF001558. GSHase. 1 hit.
SUPFAMiSSF52440. SSF52440. 1 hit.
TIGRFAMsiTIGR01986. glut_syn_euk. 1 hit.
ProtoNetiSearch...

Entry informationi

Entry nameiGSHB_HUMAN
AccessioniPrimary (citable) accession number: P48637
Secondary accession number(s): B2R697
, B6F210, E1P5P9, Q4TTD9
Entry historyi
Integrated into UniProtKB/Swiss-Prot: February 1, 1996
Last sequence update: February 1, 1996
Last modified: November 30, 2016
This is version 172 of the entry and version 1 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, Direct protein sequencing, Reference proteome

Documents

  1. Human chromosome 20
    Human chromosome 20: 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.