Skip Header

You are using a version of browser that may not display all the features of this website. Please consider upgrading your browser.

Q64568 - AT2B3_RAT

UniProt

Q64568 - AT2B3_RAT

(max 400 entries)x

Your basket is currently empty.

Select item(s) and click on "Add to basket" to create your own collection here
(400 entries max)

Protein

Plasma membrane calcium-transporting ATPase 3

Gene

Atp2b3

Organism
Rattus norvegicus (Rat)
Status
Reviewed-Annotation score: Annotation score: 5 out of 5-Experimental evidence at transcript leveli

Functioni

This magnesium-dependent enzyme catalyzes the hydrolysis of ATP coupled with the transport of calcium out of the cell.

Catalytic activityi

ATP + H2O + Ca2+(Side 1) = ADP + phosphate + Ca2+(Side 2).

Sites

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Active sitei473 – 47314-aspartylphosphate intermediateBy similarity
Metal bindingi794 – 7941MagnesiumBy similarity
Metal bindingi798 – 7981MagnesiumBy similarity

GO - Molecular functioni

  1. ATP binding Source: UniProtKB-KW
  2. calcium-transporting ATPase activity Source: UniProtKB-EC
  3. metal ion binding Source: UniProtKB-KW
  4. PDZ domain binding Source: RGD

GO - Biological processi

  1. brain development Source: RGD
  2. neural retina development Source: RGD
Complete GO annotation...

Keywords - Molecular functioni

Hydrolase

Keywords - Biological processi

Calcium transport, Ion transport, Transport

Keywords - Ligandi

ATP-binding, Calcium, Calmodulin-binding, Magnesium, Metal-binding, Nucleotide-binding

Enzyme and pathway databases

ReactomeiREACT_247493. Ion transport by P-type ATPases.
REACT_251526. Reduction of cytosolic Ca++ levels.

Names & Taxonomyi

Protein namesi
Recommended name:
Plasma membrane calcium-transporting ATPase 3 (EC:3.6.3.8)
Short name:
PMCA3
Alternative name(s):
Plasma membrane calcium ATPase isoform 3
Plasma membrane calcium pump isoform 3
Gene namesi
Name:Atp2b3
Synonyms:Pmca3
OrganismiRattus norvegicus (Rat)
Taxonomic identifieri10116 [NCBI]
Taxonomic lineageiEukaryota › Metazoa › Chordata › Craniata › Vertebrata › Euteleostomi › Mammalia › Eutheria › Euarchontoglires › Glires › Rodentia › Sciurognathi › Muroidea › Muridae › Murinae › Rattus
ProteomesiUP000002494: Chromosome 1

Organism-specific databases

RGDi621304. Atp2b3.

Subcellular locationi

Cell membrane; Multi-pass membrane protein

Topology

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Topological domaini1 – 9797CytoplasmicSequence AnalysisAdd
BLAST
Transmembranei98 – 11821HelicalSequence AnalysisAdd
BLAST
Topological domaini119 – 15537ExtracellularSequence AnalysisAdd
BLAST
Transmembranei156 – 17621HelicalSequence AnalysisAdd
BLAST
Topological domaini177 – 364188CytoplasmicSequence AnalysisAdd
BLAST
Transmembranei365 – 38420HelicalSequence AnalysisAdd
BLAST
Topological domaini385 – 41733ExtracellularSequence AnalysisAdd
BLAST
Transmembranei418 – 43518HelicalSequence AnalysisAdd
BLAST
Topological domaini436 – 849414CytoplasmicSequence AnalysisAdd
BLAST
Transmembranei850 – 86920HelicalSequence AnalysisAdd
BLAST
Topological domaini870 – 87910ExtracellularSequence Analysis
Transmembranei880 – 90021HelicalSequence AnalysisAdd
BLAST
Topological domaini901 – 92020CytoplasmicSequence AnalysisAdd
BLAST
Transmembranei921 – 94323HelicalSequence AnalysisAdd
BLAST
Topological domaini944 – 96118ExtracellularSequence AnalysisAdd
BLAST
Transmembranei962 – 98322HelicalSequence AnalysisAdd
BLAST
Topological domaini984 – 100219CytoplasmicSequence AnalysisAdd
BLAST
Transmembranei1003 – 102422HelicalSequence AnalysisAdd
BLAST
Topological domaini1025 – 103410ExtracellularSequence Analysis
Transmembranei1035 – 105622HelicalSequence AnalysisAdd
BLAST
Topological domaini1057 – 1258202CytoplasmicSequence AnalysisAdd
BLAST

GO - Cellular componenti

  1. integral component of membrane Source: UniProtKB-KW
  2. membrane raft Source: RGD
  3. plasma membrane Source: UniProtKB-SubCell
Complete GO annotation...

Keywords - Cellular componenti

Cell membrane, Membrane

PTM / Processingi

Molecule processing

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Chaini1 – 12581258Plasma membrane calcium-transporting ATPase 3PRO_0000046219Add
BLAST

Amino acid modifications

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Modified residuei1113 – 11131Phosphothreonine; by PKCBy similarity

Keywords - PTMi

Phosphoprotein

Proteomic databases

PaxDbiQ64568.
PRIDEiQ64568.

PTM databases

PhosphoSiteiQ64568.

Expressioni

Tissue specificityi

Isoform XA is the most abundant form in brain and most other tissues. Isoform XB is the most abundant form in skeletal muscle and is also found in brain and at low levels in testis and kidney. The other isoforms are only found at low levels in various tissues.

Gene expression databases

ExpressionAtlasiQ64568. baseline and differential.
GenevestigatoriQ64568.

Interactioni

Subunit structurei

Interacts with PDZD11.By similarity

Protein-protein interaction databases

BioGridi248231. 1 interaction.

Structurei

3D structure databases

ProteinModelPortaliQ64568.
ModBaseiSearch...
MobiDBiSearch...

Family & Domainsi

Region

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Regioni1097 – 111418Calmodulin-binding subdomain ABy similarityAdd
BLAST
Regioni1115 – 112410Calmodulin-binding subdomain BBy similarity

Compositional bias

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Compositional biasi297 – 3004Poly-Glu
Compositional biasi1212 – 12176Poly-Pro

Sequence similaritiesi

Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IIB subfamily. [View classification]Curated

Keywords - Domaini

Transmembrane, Transmembrane helix

Phylogenomic databases

eggNOGiCOG0474.
GeneTreeiENSGT00510000046331.
HOGENOMiHOG000265623.
HOVERGENiHBG061286.
InParanoidiQ64568.
KOiK05850.
PhylomeDBiQ64568.

Family and domain databases

Gene3Di1.20.1110.10. 3 hits.
InterProiIPR030325. ATP2B3.
IPR022141. ATP_Ca_trans_C.
IPR006068. ATPase_P-typ_cation-transptr_C.
IPR004014. ATPase_P-typ_cation-transptr_N.
IPR023299. ATPase_P-typ_cyto_domN.
IPR018303. ATPase_P-typ_P_site.
IPR023298. ATPase_P-typ_TM_dom.
IPR008250. ATPase_P-typ_transduc_dom_A.
IPR023214. HAD-like_dom.
IPR006408. P-type_ATPase_IIB.
IPR001757. P_typ_ATPase.
[Graphical view]
PANTHERiPTHR24093:SF265. PTHR24093:SF265. 1 hit.
PfamiPF12424. ATP_Ca_trans_C. 2 hits.
PF00689. Cation_ATPase_C. 1 hit.
PF00690. Cation_ATPase_N. 1 hit.
PF00122. E1-E2_ATPase. 1 hit.
PF00702. Hydrolase. 1 hit.
[Graphical view]
PRINTSiPR00119. CATATPASE.
SMARTiSM00831. Cation_ATPase_N. 1 hit.
[Graphical view]
SUPFAMiSSF56784. SSF56784. 2 hits.
SSF81660. SSF81660. 1 hit.
TIGRFAMsiTIGR01517. ATPase-IIB_Ca. 1 hit.
TIGR01494. ATPase_P-type. 3 hits.
PROSITEiPS00154. ATPASE_E1_E2. 1 hit.
[Graphical view]

Sequences (12)i

Sequence statusi: Complete.

This entry describes 12 isoformsi produced by alternative splicing. Align

Note: There is a combination of two alternative spliced domains at N-terminal site A (X and Z) and at C-terminal site C (A, B, C, D, E and F). So far the splice sites have been studied independently. Experimental confirmation may be lacking for some isoforms.

Isoform XD (identifier: Q64568-1) [UniParc]FASTAAdd to Basket

Also known as: AIICIV

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
MGDMANSSIE FHPKPQQQRE VPHVGGFGCT LAELRSLMEL RGAEALQKIQ 
        60         70         80         90        100
EAYGDVSGLC RRLKTSPTEG LADNTNDLEK RRQIYGQNFI PPKQPKTFLQ 
       110        120        130        140        150
LVWEALQDVT LIILEVAAIV SLGLSFYAPP GEESEACGNV SGGAEDEGEA 
       160        170        180        190        200
EAGWIEGAAI LLSVICVVLV TAFNDWSKEK QFRGLQSRIE QEQKFTVIRN 
       210        220        230        240        250
GQLLQVPVAA LVVGDIAQVK YGDLLPADGV LIQGNDLKID ESSLTGESDH 
       260        270        280        290        300
VRKSADKDPM LLSGTHVMEG SGRMVVTAVG VNSQTGIIFT LLGAGGEEEE 
       310        320        330        340        350
KKDKKGKQQD GAMESSQTKA KKQDGAVAME MQPLKSAEGG EMEEREKKKA 
       360        370        380        390        400
NVPKKEKSVL QGKLTKLAVQ IGKAGLVMSA ITVIILVLYF VIETFVVDGR 
       410        420        430        440        450
VWLAECTPVY VQYFVKFFII GVTVLVVAVP EGLPLAVTIS LAYSVKKMMK 
       460        470        480        490        500
DNNLVRHLDA CETMGNATAI CSDKTGTLTT NRMTVVQSYL GDTHYKEIPA 
       510        520        530        540        550
PSALTPKILD LLVHAISINS AYTTKILPPE KEGALPRQVG NKTECALLGF 
       560        570        580        590        600
ILDLKRDFQP VREQIPEDQL YKVYTFNSVR KSMSTVIRMP DGGFRLFSKG 
       610        620        630        640        650
ASEILLKKCT NILNSNGELR GFRPRDRDDM VKKIIEPMAC DGLRTICIAY 
       660        670        680        690        700
RDFSAIQEPD WDNENEVVGD LTCIAVVGIE DPVRPEVPEA IRKCQRAGIT 
       710        720        730        740        750
VRMVTGDNIN TARAIAAKCG IIQPGEDFLC LEGKEFNRRI RNEKGEIEQE 
       760        770        780        790        800
RLDKVWPKLR VLARSSPTDK HTLVKGIIDS TTGEQRQVVA VTGDGTNDGP 
       810        820        830        840        850
ALKKADVGFA MGIAGTDVAK EASDIILTDD NFTSIVKAVM WGRNVYDSIS 
       860        870        880        890        900
KFLQFQLTVN VVAVIVAFTG ACITQDSPLK AVQMLWVNLI MDTFASLALA 
       910        920        930        940        950
TEPPTESLLL RKPYGRDKPL ISRTMMKNIL GHAVYQLTII FTLLFVGELF 
       960        970        980        990       1000
FDIDSGRNAP LHSPPSEHYT IIFNTFVMMQ LFNEINARKI HGERNVFDGI 
      1010       1020       1030       1040       1050
FSNPIFCTIV LGTFGIQIVI VQFGGKPFSC SPLSTEQWLW CLFVGVGELV 
      1060       1070       1080       1090       1100
WGQVIATIPT SQLKCLKEAG HGPGKDEMTD EELAEGEEEI DHAERELRRG 
      1110       1120       1130       1140       1150
QILWFRGLNR IQTQMEVVST FKRSGSFQGA VRRRSSVLSQ LHDVTNLSTP 
      1160       1170       1180       1190       1200
THIRVVKAFR SSLYEGLEKP ESKSCIHNFM ATPEFLINDY THNIPLIDDT 
      1210       1220       1230       1240       1250
DVDENEERLR APPPPPPNQN NNAIDSGIYL TTHATKSATS SAFSSRPGSP 

LHSMETSL
Length:1,258
Mass (Da):138,559
Last modified:June 1, 2001 - v2
Checksum:i3A13781D21042BA6
GO
Isoform XA (identifier: Q64568-2) [UniParc]FASTAAdd to Basket

Also known as: AIICII

The sequence of this isoform differs from the canonical sequence as follows:
     1153-1258: IRVVKAFRSS...SPLHSMETSL → VTLSAAKPTSAAGNPSGESIP

Show »
Length:1,173
Mass (Da):128,773
Checksum:iCF49538EC579E958
GO
Isoform ZA (identifier: Q64568-3) [UniParc]FASTAAdd to Basket

Also known as: AICII

The sequence of this isoform differs from the canonical sequence as follows:
     306-319: Missing.
     1153-1258: IRVVKAFRSS...SPLHSMETSL → VTLSAAKPTSAAGNPSGESIP

Show »
Length:1,159
Mass (Da):127,297
Checksum:iA33A52545101241D
GO
Isoform XB (identifier: Q64568-4) [UniParc]FASTAAdd to Basket

Also known as: AIICI

The sequence of this isoform differs from the canonical sequence as follows:
     1115-1152: Missing.

Show »
Length:1,220
Mass (Da):134,360
Checksum:iC18A4BAEBA0362ED
GO
Isoform ZB (identifier: Q64568-5) [UniParc]FASTAAdd to Basket

Also known as: AICI

The sequence of this isoform differs from the canonical sequence as follows:
     306-319: Missing.
     1115-1152: Missing.

Show »
Length:1,206
Mass (Da):132,884
Checksum:iF83F2E1301CB4552
GO
Isoform XC (identifier: Q64568-6) [UniParc]FASTAAdd to Basket

Also known as: AIICIII

The sequence of this isoform differs from the canonical sequence as follows:
     1144-1152: Missing.

Show »
Length:1,249
Mass (Da):137,608
Checksum:i9825517A8B9744B1
GO
Isoform ZC (identifier: Q64568-7) [UniParc]FASTAAdd to Basket

Also known as: AICIII

The sequence of this isoform differs from the canonical sequence as follows:
     306-319: Missing.
     1144-1152: Missing.

Show »
Length:1,235
Mass (Da):136,132
Checksum:iDD7B43D805121FDD
GO
Isoform ZD (identifier: Q64568-8) [UniParc]FASTAAdd to Basket

Also known as: AICIV

The sequence of this isoform differs from the canonical sequence as follows:
     306-319: Missing.

Show »
Length:1,244
Mass (Da):137,083
Checksum:i3BA47725ACB4D4AE
GO
Isoform XE (identifier: Q64568-9) [UniParc]FASTAAdd to Basket

Also known as: AIICV

The sequence of this isoform differs from the canonical sequence as follows:
     1153-1258: IRVVKAFRSS...SPLHSMETSL → VTLSAAKPTSAAGSES

Show »
Length:1,168
Mass (Da):128,295
Checksum:i09F539391396F9A2
GO
Isoform ZE (identifier: Q64568-10) [UniParc]FASTAAdd to Basket

Also known as: AICV

The sequence of this isoform differs from the canonical sequence as follows:
     306-319: Missing.
     1153-1258: IRVVKAFRSS...SPLHSMETSL → VTLSAAKPTSAAGSES

Show »
Length:1,154
Mass (Da):126,818
Checksum:i81387C79448BCC0F
GO
Isoform XF (identifier: Q64568-11) [UniParc]FASTAAdd to Basket

Also known as: AIICVI

The sequence of this isoform differs from the canonical sequence as follows:
     1115-1258: MEVVSTFKRS...SPLHSMETSL → VCWDGKKMLRTTEVG

Show »
Length:1,129
Mass (Da):124,342
Checksum:i7B4F423A0C709026
GO
Isoform ZF (identifier: Q64568-12) [UniParc]FASTAAdd to Basket

Also known as: AICVI

The sequence of this isoform differs from the canonical sequence as follows:
     306-319: Missing.
     1115-1258: MEVVSTFKRS...SPLHSMETSL → VCWDGKKMLRTTEVG

Show »
Length:1,115
Mass (Da):122,866
Checksum:i1A545F41D1A951EB
GO

Alternative sequence

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Alternative sequencei306 – 31914Missing in isoform ZA, isoform ZB, isoform ZC, isoform ZD, isoform ZE and isoform ZF. 1 PublicationVSP_000396Add
BLAST
Alternative sequencei1115 – 1258144MEVVS…METSL → VCWDGKKMLRTTEVG in isoform XF and isoform ZF. CuratedVSP_000398Add
BLAST
Alternative sequencei1115 – 115238Missing in isoform XB and isoform ZB. CuratedVSP_000397Add
BLAST
Alternative sequencei1144 – 11529Missing in isoform XC and isoform ZC. CuratedVSP_000399
Alternative sequencei1153 – 1258106IRVVK…METSL → VTLSAAKPTSAAGNPSGESI P in isoform XA and isoform ZA. 1 PublicationVSP_000400Add
BLAST
Alternative sequencei1153 – 1258106IRVVK…METSL → VTLSAAKPTSAAGSES in isoform XE and isoform ZE. CuratedVSP_000401Add
BLAST

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
L05565, L05558, L05564 Genomic DNA. Translation: AAA53650.1.
J05087 mRNA. Translation: AAA69667.1.
M96626 mRNA. Translation: AAA50821.1.
PIRiA34308.
C44525.
RefSeqiNP_579822.1. NM_133288.1. [Q64568-3]
XP_008771842.1. XM_008773620.1. [Q64568-7]
XP_008771844.1. XM_008773622.1. [Q64568-5]
UniGeneiRn.11053.

Genome annotation databases

EnsembliENSRNOT00000023934; ENSRNOP00000023934; ENSRNOG00000017798. [Q64568-3]
GeneIDi29599.
KEGGirno:29599.

Keywords - Coding sequence diversityi

Alternative splicing

Cross-referencesi

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
L05565, L05558, L05564 Genomic DNA. Translation: AAA53650.1.
J05087 mRNA. Translation: AAA69667.1.
M96626 mRNA. Translation: AAA50821.1.
PIRiA34308.
C44525.
RefSeqiNP_579822.1. NM_133288.1. [Q64568-3]
XP_008771842.1. XM_008773620.1. [Q64568-7]
XP_008771844.1. XM_008773622.1. [Q64568-5]
UniGeneiRn.11053.

3D structure databases

ProteinModelPortaliQ64568.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

BioGridi248231. 1 interaction.

PTM databases

PhosphoSiteiQ64568.

Proteomic databases

PaxDbiQ64568.
PRIDEiQ64568.

Protocols and materials databases

Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsembliENSRNOT00000023934; ENSRNOP00000023934; ENSRNOG00000017798. [Q64568-3]
GeneIDi29599.
KEGGirno:29599.

Organism-specific databases

CTDi492.
RGDi621304. Atp2b3.

Phylogenomic databases

eggNOGiCOG0474.
GeneTreeiENSGT00510000046331.
HOGENOMiHOG000265623.
HOVERGENiHBG061286.
InParanoidiQ64568.
KOiK05850.
PhylomeDBiQ64568.

Enzyme and pathway databases

ReactomeiREACT_247493. Ion transport by P-type ATPases.
REACT_251526. Reduction of cytosolic Ca++ levels.

Miscellaneous databases

NextBioi609754.
PROiQ64568.

Gene expression databases

ExpressionAtlasiQ64568. baseline and differential.
GenevestigatoriQ64568.

Family and domain databases

Gene3Di1.20.1110.10. 3 hits.
InterProiIPR030325. ATP2B3.
IPR022141. ATP_Ca_trans_C.
IPR006068. ATPase_P-typ_cation-transptr_C.
IPR004014. ATPase_P-typ_cation-transptr_N.
IPR023299. ATPase_P-typ_cyto_domN.
IPR018303. ATPase_P-typ_P_site.
IPR023298. ATPase_P-typ_TM_dom.
IPR008250. ATPase_P-typ_transduc_dom_A.
IPR023214. HAD-like_dom.
IPR006408. P-type_ATPase_IIB.
IPR001757. P_typ_ATPase.
[Graphical view]
PANTHERiPTHR24093:SF265. PTHR24093:SF265. 1 hit.
PfamiPF12424. ATP_Ca_trans_C. 2 hits.
PF00689. Cation_ATPase_C. 1 hit.
PF00690. Cation_ATPase_N. 1 hit.
PF00122. E1-E2_ATPase. 1 hit.
PF00702. Hydrolase. 1 hit.
[Graphical view]
PRINTSiPR00119. CATATPASE.
SMARTiSM00831. Cation_ATPase_N. 1 hit.
[Graphical view]
SUPFAMiSSF56784. SSF56784. 2 hits.
SSF81660. SSF81660. 1 hit.
TIGRFAMsiTIGR01517. ATPase-IIB_Ca. 1 hit.
TIGR01494. ATPase_P-type. 3 hits.
PROSITEiPS00154. ATPASE_E1_E2. 1 hit.
[Graphical view]
ProtoNetiSearch...

Publicationsi

  1. "Molecular cloning of a third isoform of the calmodulin-sensitive plasma membrane Ca2+-transporting ATPase that is expressed predominantly in brain and skeletal muscle."
    Greeb J., Shull G.E.
    J. Biol. Chem. 264:18569-18576(1989) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA] (ISOFORM ZA).
    Tissue: Brain.
  2. "Structure of the rat plasma membrane Ca(2+)-ATPase isoform 3 gene and characterization of alternative splicing and transcription products. Skeletal muscle-specific splicing results in a plasma membrane Ca(2+)-ATPase with a novel calmodulin-binding domain."
    Burk S.E., Shull G.E.
    J. Biol. Chem. 267:19683-19690(1992) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA] OF 1016-1258 (ISOFORMS XF/ZF), ALTERNATIVE SPLICING.
    Strain: CD Charles River.
  3. "Alternative splicing of exons encoding the calmodulin-binding domains and C termini of plasma membrane Ca(2+)-ATPase isoforms 1, 2, 3, and 4."
    Keeton T.P., Burk S.E., Shull G.E.
    J. Biol. Chem. 268:2740-2748(1993) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [GENOMIC DNA] OF 1054-1258, ALTERNATIVE SPLICING (ISOFORMS XA/ZA).
    Strain: CD Charles River.
+Additional computationally mapped references.

Entry informationi

Entry nameiAT2B3_RAT
AccessioniPrimary (citable) accession number: Q64568
Secondary accession number(s): Q01489, Q63444
Entry historyi
Integrated into UniProtKB/Swiss-Prot: June 1, 2001
Last sequence update: June 1, 2001
Last modified: January 7, 2015
This is version 127 of the entry and version 2 of the sequence. [Complete history]
Entry statusiReviewed (UniProtKB/Swiss-Prot)
Annotation programChordata Protein Annotation Program

Miscellaneousi

Keywords - Technical termi

Complete proteome, Reference proteome

Documents

  1. 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.