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Protein

Voltage-gated potassium channel subunit beta-2

Gene

KCNAB2

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

Functioni

Cytoplasmic potassium channel subunit that modulates the characteristics of the channel-forming alpha-subunits (PubMed:7649300, PubMed:11825900). Contributes to the regulation of nerve signaling, and prevents neuronal hyperexcitability (By similarity). Promotes expression of the pore-forming alpha subunits at the cell membrane, and thereby increases channel activity (By similarity). Promotes potassium channel closure via a mechanism that does not involve physical obstruction of the channel pore (PubMed:7649300, PubMed:11825900). Promotes KCNA4 channel closure (PubMed:7649300, PubMed:11825900). Modulates the functional properties of KCNA5 (By similarity). Enhances KCNB2 channel activity (By similarity). Binds NADPH and has NADPH-dependent aldoketoreductase activity (By similarity). Has broad substrate specificity and can catalyze the reduction of methylglyoxal, 9,10-phenanthrenequinone, prostaglandin J2, 4-nitrobenzaldehyde, 4-nitroacetophenone and 4-oxo-trans-2-nonenal (in vitro) (By similarity).By similarity2 Publications

Sites

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Binding sitei63NADP1 Publication1
Binding sitei85NADP1 Publication1
Active sitei90Proton donor/acceptorBy similarity1
Binding sitei90NADP1 Publication1
Binding sitei214NADP1 Publication1
Binding sitei254NADP1 Publication1

Regions

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Nucleotide bindingi56 – 57NADP1 Publication2
Nucleotide bindingi188 – 189NADP1 Publication2
Nucleotide bindingi243 – 248NADP1 Publication6
Nucleotide bindingi323 – 329NADP1 Publication7

GO - Molecular functioni

GO - Biological processi

Complete GO annotation...

Keywords - Molecular functioni

Ion channel, Oxidoreductase, Voltage-gated channel

Keywords - Biological processi

Ion transport, Potassium transport, Transport

Keywords - Ligandi

NADP, Potassium

Enzyme and pathway databases

BioCyciZFISH:ENSG00000069424-MONOMER.
ReactomeiR-HSA-1296072. Voltage gated Potassium channels.
R-HSA-6798695. Neutrophil degranulation.

Names & Taxonomyi

Protein namesi
Recommended name:
Voltage-gated potassium channel subunit beta-2 (EC:1.1.1.-By similarity)
Alternative name(s):
K(+) channel subunit beta-2
Kv-beta-2
Short name:
hKvbeta2
Gene namesi
Name:KCNAB2
Synonyms:KCNA2B, KCNK2
OrganismiHomo sapiens (Human)
Taxonomic identifieri9606 [NCBI]
Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresPrimatesHaplorrhiniCatarrhiniHominidaeHomo
Proteomesi
  • UP000005640 Componenti: Chromosome 1

Organism-specific databases

HGNCiHGNC:6229. KCNAB2.

Subcellular locationi

GO - Cellular componenti

  • axon terminus Source: Ensembl
  • cell junction Source: UniProtKB-KW
  • cytoskeleton Source: UniProtKB-SubCell
  • cytosol Source: UniProtKB
  • extrinsic component of cytoplasmic side of plasma membrane Source: UniProtKB
  • juxtaparanode region of axon Source: UniProtKB
  • membrane Source: UniProtKB
  • pinceau fiber Source: UniProtKB
  • plasma membrane Source: Reactome
  • postsynaptic density Source: Ensembl
  • voltage-gated potassium channel complex Source: UniProtKB
Complete GO annotation...

Keywords - Cellular componenti

Cell junction, Cell membrane, Cell projection, Cytoplasm, Cytoskeleton, Membrane, Synapse, Synaptosome

Pathology & Biotechi

Mutagenesis

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Mutagenesisi90Y → F: No effect on its activity in promoting KCNA4 channel closure. 1 Publication1

Organism-specific databases

DisGeNETi8514.
MalaCardsiKCNAB2.
OpenTargetsiENSG00000069424.
Orphaneti1606. 1p36 deletion syndrome.
PharmGKBiPA373.

Polymorphism and mutation databases

BioMutaiKCNAB2.
DMDMi18202496.

PTM / Processingi

Molecule processing

Feature keyPosition(s)DescriptionActionsGraphical viewLength
ChainiPRO_00001487461 – 367Voltage-gated potassium channel subunit beta-2Add BLAST367

Amino acid modifications

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Modified residuei9PhosphoserineCombined sources1
Modified residuei14PhosphoserineCombined sources1
Modified residuei20PhosphoserineBy similarity1
Modified residuei28Asymmetric dimethylarginine; alternateCombined sources1
Modified residuei28Omega-N-methylarginine; alternateBy similarity1
Modified residuei31Phosphoserine1 Publication1
Modified residuei112Phosphoserine1 Publication1
Modified residuei124N6-acetyllysineCombined sources1

Post-translational modificationi

Phosphorylated by PRKCZ; may be regulated by incorporation in a complex composed of PRKCZ and SQSTM1.By similarity

Keywords - PTMi

Acetylation, Methylation, Phosphoprotein

Proteomic databases

EPDiQ13303.
MaxQBiQ13303.
PaxDbiQ13303.
PeptideAtlasiQ13303.
PRIDEiQ13303.

PTM databases

iPTMnetiQ13303.
PhosphoSitePlusiQ13303.

Expressioni

Tissue specificityi

Detected in myelinated nerve fibers in the spinal cord, in the juxtaparanodal region of the nodes of Ranvier, but also in the paranodal region (PubMed:11086297). Detected in hippocampus (at protein level) (PubMed:21357749). Detected in hippocampus (PubMed:7649300).3 Publications

Gene expression databases

BgeeiENSG00000069424.
CleanExiHS_KCNAB2.
HS_KCNK2.
ExpressionAtlasiQ13303. baseline and differential.
GenevisibleiQ13303. HS.

Organism-specific databases

HPAiCAB001975.
HPA030185.

Interactioni

Subunit structurei

Homotetramer (By similarity). Interaction with tetrameric potassium channel alpha subunits gives rise to a heterooctamer (By similarity). Identified in potassium channel complexes containing KCNA1, KCNA2, KCNA4, KCNA5, KCNA6, KCNAB1 and KCNAB2 (By similarity). Interacts with KCNA1 (PubMed:11086297). Interacts with KCNA2 (PubMed:11086297). Interacts with KCNA4 and KCND3 (By similarity). Interacts with KCNA5 (By similarity). Interacts with KCNB2 (By similarity). Interacts (in unphosphorylated form) with MAPRE1 (By similarity). Forms a ternary complex with SQSTM1 and PRKCZ (By similarity).By similarity1 Publication

Protein-protein interaction databases

BioGridi114086. 36 interactors.
IntActiQ13303. 13 interactors.
MINTiMINT-2865320.
STRINGi9606.ENSP00000367323.

Structurei

Secondary structure

1367
Legend: HelixTurnBeta strandPDB Structure known for this area
Show more details
Feature keyPosition(s)DescriptionActionsGraphical viewLength
Beta strandi39 – 42Combined sources4
Beta strandi48 – 55Combined sources8
Helixi59 – 63Combined sources5
Helixi66 – 78Combined sources13
Beta strandi83 – 85Combined sources3
Helixi90 – 93Combined sources4
Helixi94 – 106Combined sources13
Helixi110 – 112Combined sources3
Beta strandi114 – 121Combined sources8
Helixi126 – 128Combined sources3
Beta strandi129 – 131Combined sources3
Helixi133 – 147Combined sources15
Beta strandi152 – 159Combined sources8
Helixi166 – 178Combined sources13
Beta strandi181 – 189Combined sources9
Helixi192 – 205Combined sources14
Beta strandi212 – 216Combined sources5
Helixi223 – 226Combined sources4
Helixi228 – 236Combined sources9
Beta strandi239 – 243Combined sources5
Helixi247 – 252Combined sources6
Turni253 – 257Combined sources5
Helixi264 – 266Combined sources3
Helixi271 – 277Combined sources7
Helixi280 – 299Combined sources20
Helixi303 – 313Combined sources11
Beta strandi317 – 322Combined sources6
Helixi327 – 334Combined sources8
Helixi336 – 339Combined sources4
Helixi340 – 342Combined sources3
Helixi345 – 355Combined sources11

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
PDB entryMethodResolution (Å)ChainPositionsPDBsum
1ZSXX-ray1.90A39-360[»]
ProteinModelPortaliQ13303.
SMRiQ13303.
ModBaseiSearch...
MobiDBiSearch...

Miscellaneous databases

EvolutionaryTraceiQ13303.

Family & Domainsi

Domaini

In contrast to KCNAB1, the shorter N-terminal domain of KCNAB2 cannot mediate closure of delayed rectifier potassium channels by physically obstructing the pore.1 Publication

Sequence similaritiesi

Phylogenomic databases

eggNOGiKOG1575. Eukaryota.
COG0667. LUCA.
GeneTreeiENSGT00550000074567.
HOGENOMiHOG000250283.
HOVERGENiHBG052216.
InParanoidiQ13303.
KOiK04883.
OMAiCINNLEF.
OrthoDBiEOG091G0KDN.
PhylomeDBiQ13303.
TreeFamiTF324563.

Family and domain databases

CDDicd06660. Aldo_ket_red. 1 hit.
Gene3Di3.20.20.100. 1 hit.
InterProiIPR001395. Aldo/ket_red/Kv-b.
IPR005983. K_chnl_volt-dep_bsu_KCNAB.
IPR005399. K_chnl_volt-dep_bsu_KCNAB-rel.
IPR005401. K_chnl_volt-dep_bsu_KCNAB2.
IPR023210. NADP_OxRdtase_dom.
[Graphical view]
PANTHERiPTHR11732. PTHR11732. 1 hit.
PfamiPF00248. Aldo_ket_red. 1 hit.
[Graphical view]
PRINTSiPR01579. KCNAB2CHANEL.
PR01577. KCNABCHANNEL.
SUPFAMiSSF51430. SSF51430. 1 hit.
TIGRFAMsiTIGR01293. Kv_beta. 1 hit.

Sequences (5)i

Sequence statusi: Complete.

This entry describes 5 isoformsi produced by alternative splicing. AlignAdd to basket

Isoform 1 (identifier: Q13303-1) [UniParc]FASTAAdd to basket
Also known as: KvB2.1

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
MYPESTTGSP ARLSLRQTGS PGMIYSTRYG SPKRQLQFYR NLGKSGLRVS
60 70 80 90 100
CLGLGTWVTF GGQITDEMAE QLMTLAYDNG INLFDTAEVY AAGKAEVVLG
110 120 130 140 150
NIIKKKGWRR SSLVITTKIF WGGKAETERG LSRKHIIEGL KASLERLQLE
160 170 180 190 200
YVDVVFANRP DPNTPMEETV RAMTHVINQG MAMYWGTSRW SSMEIMEAYS
210 220 230 240 250
VARQFNLTPP ICEQAEYHMF QREKVEVQLP ELFHKIGVGA MTWSPLACGI
260 270 280 290 300
VSGKYDSGIP PYSRASLKGY QWLKDKILSE EGRRQQAKLK ELQAIAERLG
310 320 330 340 350
CTLPQLAIAW CLRNEGVSSV LLGASNADQL MENIGAIQVL PKLSSSIIHE
360
IDSILGNKPY SKKDYRS
Length:367
Mass (Da):41,000
Last modified:January 1, 1998 - v2
Checksum:i91A673F8992140DA
GO
Isoform 2 (identifier: Q13303-2) [UniParc]FASTAAdd to basket
Also known as: KvB2.2

The sequence of this isoform differs from the canonical sequence as follows:
     26-39: Missing.

Show »
Length:353
Mass (Da):39,287
Checksum:i7D59C8203AC5606F
GO
Isoform 3 (identifier: Q13303-3) [UniParc]FASTAAdd to basket

The sequence of this isoform differs from the canonical sequence as follows:
     1-38: MYPESTTGSP...YGSPKRQLQF → MLSMTYSESL...GCTAQRTGMK
     167-167: E → EGDPFSSSKSRTFIIE

Show »
Length:415
Mass (Da):46,527
Checksum:i3AD46E32E4B200AF
GO
Isoform 4 (identifier: Q13303-4) [UniParc]FASTAAdd to basket

The sequence of this isoform differs from the canonical sequence as follows:
     1-67: Missing.

Show »
Length:300
Mass (Da):33,657
Checksum:i3ADDAAE15216B737
GO
Isoform 5 (identifier: Q13303-5) [UniParc]FASTAAdd to basket

The sequence of this isoform differs from the canonical sequence as follows:
     340-367: LPKLSSSIIHEIDSILGNKPYSKKDYRS → RVRGPAGQRA...GELAFQQEQT

Note: No experimental confirmation available.
Show »
Length:395
Mass (Da):43,560
Checksum:i4E6CED2B3028BBB0
GO

Natural variant

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Natural variantiVAR_04874788E → K.Corresponds to variant rs2229003dbSNPEnsembl.1

Alternative sequence

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Alternative sequenceiVSP_0443111 – 67Missing in isoform 4. 1 PublicationAdd BLAST67
Alternative sequenceiVSP_0411891 – 38MYPES…RQLQF → MLSMTYSESLRSVSSRCHSE WALHPVRQTDTLELQRLREV RAAAQARNMESFLRMHGLSL DGCTAQRTGMK in isoform 3. 1 PublicationAdd BLAST38
Alternative sequenceiVSP_00105426 – 39Missing in isoform 2. 1 PublicationAdd BLAST14
Alternative sequenceiVSP_041190167E → EGDPFSSSKSRTFIIE in isoform 3. 1 Publication1
Alternative sequenceiVSP_057282340 – 367LPKLS…KDYRS → RVRGPAGQRAHPSPSPVQCI LPGSSCVPGSVLGTQDAPVN HQSCAPGELAFQQEQT in isoform 5. 1 PublicationAdd BLAST28

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
U33429 mRNA. Translation: AAC50955.1.
AF029749 mRNA. Translation: AAB84170.1.
AF044253 mRNA. Translation: AAB99859.1.
AK124696 mRNA. Translation: BAG54071.1.
AK131252 mRNA. Translation: BAD18431.1.
AK289819 mRNA. Translation: BAF82508.1.
AK315858 mRNA. Translation: BAF98749.1.
AL035406 Genomic DNA. Translation: CAC08512.1.
AL035406 Genomic DNA. Translation: CAI19885.1.
BC110351 mRNA. Translation: AAI10352.1.
BC126424 mRNA. Translation: AAI26425.1.
BC130413 mRNA. Translation: AAI30414.1.
CCDSiCCDS55.1. [Q13303-1]
CCDS55570.1. [Q13303-3]
CCDS55571.1. [Q13303-4]
CCDS56.1. [Q13303-2]
PIRiS66502.
RefSeqiNP_001186789.1. NM_001199860.1. [Q13303-1]
NP_001186790.1. NM_001199861.1. [Q13303-1]
NP_001186791.1. NM_001199862.1. [Q13303-3]
NP_001186792.1. NM_001199863.1. [Q13303-4]
NP_003627.1. NM_003636.3. [Q13303-1]
NP_742128.1. NM_172130.2. [Q13303-2]
XP_005263571.1. XM_005263514.2. [Q13303-2]
XP_011540623.1. XM_011542321.2. [Q13303-5]
XP_011540624.1. XM_011542322.2. [Q13303-5]
UniGeneiHs.440497.
Hs.735032.

Genome annotation databases

EnsembliENST00000164247; ENSP00000164247; ENSG00000069424. [Q13303-1]
ENST00000341524; ENSP00000340824; ENSG00000069424. [Q13303-1]
ENST00000352527; ENSP00000318772; ENSG00000069424. [Q13303-2]
ENST00000378083; ENSP00000367323; ENSG00000069424. [Q13303-3]
ENST00000378092; ENSP00000367332; ENSG00000069424. [Q13303-2]
ENST00000378097; ENSP00000367337; ENSG00000069424. [Q13303-1]
ENST00000458166; ENSP00000396167; ENSG00000069424. [Q13303-4]
ENST00000602612; ENSP00000473602; ENSG00000069424. [Q13303-5]
GeneIDi8514.
KEGGihsa:8514.
UCSCiuc001alv.3. human. [Q13303-1]

Keywords - Coding sequence diversityi

Alternative splicing, Polymorphism

Cross-referencesi

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
U33429 mRNA. Translation: AAC50955.1.
AF029749 mRNA. Translation: AAB84170.1.
AF044253 mRNA. Translation: AAB99859.1.
AK124696 mRNA. Translation: BAG54071.1.
AK131252 mRNA. Translation: BAD18431.1.
AK289819 mRNA. Translation: BAF82508.1.
AK315858 mRNA. Translation: BAF98749.1.
AL035406 Genomic DNA. Translation: CAC08512.1.
AL035406 Genomic DNA. Translation: CAI19885.1.
BC110351 mRNA. Translation: AAI10352.1.
BC126424 mRNA. Translation: AAI26425.1.
BC130413 mRNA. Translation: AAI30414.1.
CCDSiCCDS55.1. [Q13303-1]
CCDS55570.1. [Q13303-3]
CCDS55571.1. [Q13303-4]
CCDS56.1. [Q13303-2]
PIRiS66502.
RefSeqiNP_001186789.1. NM_001199860.1. [Q13303-1]
NP_001186790.1. NM_001199861.1. [Q13303-1]
NP_001186791.1. NM_001199862.1. [Q13303-3]
NP_001186792.1. NM_001199863.1. [Q13303-4]
NP_003627.1. NM_003636.3. [Q13303-1]
NP_742128.1. NM_172130.2. [Q13303-2]
XP_005263571.1. XM_005263514.2. [Q13303-2]
XP_011540623.1. XM_011542321.2. [Q13303-5]
XP_011540624.1. XM_011542322.2. [Q13303-5]
UniGeneiHs.440497.
Hs.735032.

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
PDB entryMethodResolution (Å)ChainPositionsPDBsum
1ZSXX-ray1.90A39-360[»]
ProteinModelPortaliQ13303.
SMRiQ13303.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

BioGridi114086. 36 interactors.
IntActiQ13303. 13 interactors.
MINTiMINT-2865320.
STRINGi9606.ENSP00000367323.

PTM databases

iPTMnetiQ13303.
PhosphoSitePlusiQ13303.

Polymorphism and mutation databases

BioMutaiKCNAB2.
DMDMi18202496.

Proteomic databases

EPDiQ13303.
MaxQBiQ13303.
PaxDbiQ13303.
PeptideAtlasiQ13303.
PRIDEiQ13303.

Protocols and materials databases

DNASUi8514.
Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsembliENST00000164247; ENSP00000164247; ENSG00000069424. [Q13303-1]
ENST00000341524; ENSP00000340824; ENSG00000069424. [Q13303-1]
ENST00000352527; ENSP00000318772; ENSG00000069424. [Q13303-2]
ENST00000378083; ENSP00000367323; ENSG00000069424. [Q13303-3]
ENST00000378092; ENSP00000367332; ENSG00000069424. [Q13303-2]
ENST00000378097; ENSP00000367337; ENSG00000069424. [Q13303-1]
ENST00000458166; ENSP00000396167; ENSG00000069424. [Q13303-4]
ENST00000602612; ENSP00000473602; ENSG00000069424. [Q13303-5]
GeneIDi8514.
KEGGihsa:8514.
UCSCiuc001alv.3. human. [Q13303-1]

Organism-specific databases

CTDi8514.
DisGeNETi8514.
GeneCardsiKCNAB2.
HGNCiHGNC:6229. KCNAB2.
HPAiCAB001975.
HPA030185.
MalaCardsiKCNAB2.
MIMi601142. gene.
neXtProtiNX_Q13303.
OpenTargetsiENSG00000069424.
Orphaneti1606. 1p36 deletion syndrome.
PharmGKBiPA373.
GenAtlasiSearch...

Phylogenomic databases

eggNOGiKOG1575. Eukaryota.
COG0667. LUCA.
GeneTreeiENSGT00550000074567.
HOGENOMiHOG000250283.
HOVERGENiHBG052216.
InParanoidiQ13303.
KOiK04883.
OMAiCINNLEF.
OrthoDBiEOG091G0KDN.
PhylomeDBiQ13303.
TreeFamiTF324563.

Enzyme and pathway databases

BioCyciZFISH:ENSG00000069424-MONOMER.
ReactomeiR-HSA-1296072. Voltage gated Potassium channels.
R-HSA-6798695. Neutrophil degranulation.

Miscellaneous databases

ChiTaRSiKCNAB2. human.
EvolutionaryTraceiQ13303.
GeneWikiiKCNAB2.
GenomeRNAii8514.
PROiQ13303.
SOURCEiSearch...

Gene expression databases

BgeeiENSG00000069424.
CleanExiHS_KCNAB2.
HS_KCNK2.
ExpressionAtlasiQ13303. baseline and differential.
GenevisibleiQ13303. HS.

Family and domain databases

CDDicd06660. Aldo_ket_red. 1 hit.
Gene3Di3.20.20.100. 1 hit.
InterProiIPR001395. Aldo/ket_red/Kv-b.
IPR005983. K_chnl_volt-dep_bsu_KCNAB.
IPR005399. K_chnl_volt-dep_bsu_KCNAB-rel.
IPR005401. K_chnl_volt-dep_bsu_KCNAB2.
IPR023210. NADP_OxRdtase_dom.
[Graphical view]
PANTHERiPTHR11732. PTHR11732. 1 hit.
PfamiPF00248. Aldo_ket_red. 1 hit.
[Graphical view]
PRINTSiPR01579. KCNAB2CHANEL.
PR01577. KCNABCHANNEL.
SUPFAMiSSF51430. SSF51430. 1 hit.
TIGRFAMsiTIGR01293. Kv_beta. 1 hit.
ProtoNetiSearch...

Entry informationi

Entry nameiKCAB2_HUMAN
AccessioniPrimary (citable) accession number: Q13303
Secondary accession number(s): A0AVM9
, A8K1A4, B0AZR7, O43659, Q2YD85, Q5TG82, Q5TG83, Q6ZNE4, Q99411
Entry historyi
Integrated into UniProtKB/Swiss-Prot: October 18, 2001
Last sequence update: January 1, 1998
Last modified: November 30, 2016
This is version 164 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, Reference proteome

Documents

  1. Human chromosome 1
    Human chromosome 1: 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. PDB cross-references
    Index of Protein Data Bank (PDB) cross-references
  6. 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.