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Protein

Kallikrein-6

Gene

KLK6

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

Functioni

Serine protease which exhibits a preference for Arg over Lys in the substrate P1 position and for Ser or Pro in the P2 position. Shows activity against amyloid precursor protein, myelin basic protein, gelatin, casein and extracellular matrix proteins such as fibronectin, laminin, vitronectin and collagen. Degrades alpha-synuclein and prevents its polymerization, indicating that it may be involved in the pathogenesis of Parkinson disease and other synucleinopathies. May be involved in regulation of axon outgrowth following spinal cord injury. Tumor cells treated with a neutralizing KLK6 antibody migrate less than control cells, suggesting a role in invasion and metastasis.6 Publications

Enzyme regulationi

Inhibited by a range of serine protease inhibitors including soybean trypsin inhibitor, benzamidine and serpins. Activated by a range of glycosaminoglycans including chondroitin sulfate, dermatan sulfate, heparan sulfate and heparin.2 Publications

Kineticsi

  1. KM=1562 µM for Tosyl-Gly-Pro-Arg-AMC2 Publications
  2. KM=777 µM for Tosyl-Gly-Pro-Lys-AMC2 Publications
  3. KM=0.410 mM for Phe-Ser-Arg-AMC2 Publications
  4. KM=0.455 mM for Gly-Gly-Arg-AMC2 Publications
  5. KM=0.335 mM for Asp-Pro-Arg-AMC2 Publications
  6. KM=0.758 mM for Gln-Gly-Arg-AMC2 Publications
  7. KM=0.625 mM for Pro-Phe-Arg-AMC2 Publications
  8. KM=0.271 mM for Val-Pro-Arg-AMC2 Publications
  9. KM=1.72 mM for Val-Leu-Lys-AMC2 Publications

    Sites

    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Active sitei62Charge relay system1 Publication1
    Active sitei106Charge relay system1 Publication1
    Active sitei197Charge relay system1 Publication1

    GO - Molecular functioni

    • serine-type endopeptidase activity Source: UniProtKB

    GO - Biological processi

    • amyloid precursor protein metabolic process Source: UniProtKB
    • central nervous system development Source: UniProtKB
    • collagen catabolic process Source: UniProtKB
    • hormone metabolic process Source: UniProtKB
    • myelination Source: UniProtKB
    • neuron death Source: UniProtKB
    • positive regulation of G-protein coupled receptor protein signaling pathway Source: UniProtKB
    • protein autoprocessing Source: UniProtKB
    • protein processing Source: GO_Central
    • regulation of cell differentiation Source: UniProtKB
    • regulation of neuron projection development Source: Ensembl
    • response to wounding Source: UniProtKB
    • tissue regeneration Source: UniProtKB
    Complete GO annotation...

    Keywords - Molecular functioni

    Hydrolase, Protease, Serine protease

    Enzyme and pathway databases

    BioCyciZFISH:ENSG00000167755-MONOMER.
    BRENDAi3.4.21.104. 2681.
    3.4.21.34. 2681.
    3.4.21.B10. 2681.
    SABIO-RKQ92876.

    Protein family/group databases

    MEROPSiS01.236.

    Names & Taxonomyi

    Protein namesi
    Recommended name:
    Kallikrein-6 (EC:3.4.21.-)
    Alternative name(s):
    Neurosin
    Protease M
    SP59
    Serine protease 18
    Serine protease 9
    Zyme
    Gene namesi
    Name:KLK6
    Synonyms:PRSS18, PRSS9
    OrganismiHomo sapiens (Human)
    Taxonomic identifieri9606 [NCBI]
    Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresPrimatesHaplorrhiniCatarrhiniHominidaeHomo
    Proteomesi
    • UP000005640 Componenti: Chromosome 19

    Organism-specific databases

    HGNCiHGNC:6367. KLK6.

    Subcellular locationi

    • Secreted
    • Nucleusnucleolus
    • Cytoplasm
    • Mitochondrion
    • Microsome

    • Note: In brain, detected in the nucleus of glial cells and in the nucleus and cytoplasm of neurons. Detected in the mitochondrial and microsomal fractions of HEK-293 cells and released into the cytoplasm following cell stress.

    GO - Cellular componenti

    • cytoplasm Source: UniProtKB
    • endoplasmic reticulum Source: UniProtKB-KW
    • extracellular region Source: UniProtKB
    • extracellular space Source: UniProtKB
    • intercellular bridge Source: HPA
    • microtubule cytoskeleton Source: HPA
    • mitochondrion Source: UniProtKB-SubCell
    • nuclear membrane Source: HPA
    • nucleolus Source: UniProtKB-SubCell
    • nucleoplasm Source: HPA
    Complete GO annotation...

    Keywords - Cellular componenti

    Cytoplasm, Endoplasmic reticulum, Microsome, Mitochondrion, Nucleus, Secreted

    Pathology & Biotechi

    Organism-specific databases

    DisGeNETi5653.
    OpenTargetsiENSG00000167755.
    PharmGKBiPA30156.

    Chemistry databases

    ChEMBLiCHEMBL4448.
    GuidetoPHARMACOLOGYi2376.

    Polymorphism and mutation databases

    BioMutaiKLK6.
    DMDMi3914480.

    PTM / Processingi

    Molecule processing

    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Signal peptidei1 – 16Sequence analysisAdd BLAST16
    PropeptideiPRO_000002794017 – 21Activation peptideSequence analysis5
    ChainiPRO_000002794122 – 244Kallikrein-6Add BLAST223

    Amino acid modifications

    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Disulfide bondi28 ↔ 157
    Disulfide bondi47 ↔ 63
    Disulfide bondi131 ↔ 231
    Glycosylationi134N-linked (GlcNAc...)Sequence analysis1
    Disulfide bondi138 ↔ 203
    Disulfide bondi168 ↔ 182
    Disulfide bondi193 ↔ 218

    Post-translational modificationi

    Inactivated by autolytic cleavage after Arg-80.

    Sites

    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Sitei80 – 81Cleavage; by autolysis2

    Keywords - PTMi

    Autocatalytic cleavage, Cleavage on pair of basic residues, Disulfide bond, Glycoprotein, Zymogen

    Proteomic databases

    MaxQBiQ92876.
    PaxDbiQ92876.
    PeptideAtlasiQ92876.
    PRIDEiQ92876.

    PTM databases

    PhosphoSitePlusiQ92876.
    UniCarbKBiQ92876.

    Miscellaneous databases

    PMAP-CutDBQ92876.

    Expressioni

    Tissue specificityi

    In fluids, highest levels found in milk of lactating women followed by cerebrospinal fluid, nipple aspirate fluid and breast cyst fluid. Also found in serum, seminal plasma and some amniotic fluids and breast tumor cytosolic extracts. Not detected in urine. At the tissue level, highest concentrations found in glandular tissues such as salivary glands followed by lung, colon, fallopian tube, placenta, breast, pituitary and kidney. Not detected in skin, spleen, bone, thyroid, heart, ureter, liver, muscle, endometrium, testis, pancreas, seminal vesicle, ovary, adrenals and prostate. In brain, detected in gray matter neurons (at protein level). Colocalizes with pathological inclusions such as Lewy bodies and glial cytoplasmic inclusions. Overexpressed in primary breast tumors but not expressed in metastatic tumors.5 Publications

    Inductioni

    By spinal cord injury. This effect is particularly prominent in macrophages, microglia and reactive astrocytes.1 Publication

    Gene expression databases

    BgeeiENSG00000167755.
    CleanExiHS_KLK6.
    ExpressionAtlasiQ92876. baseline and differential.
    GenevisibleiQ92876. HS.

    Organism-specific databases

    HPAiHPA051837.

    Interactioni

    Protein-protein interaction databases

    BioGridi111634. 12 interactors.
    IntActiQ92876. 16 interactors.
    STRINGi9606.ENSP00000309148.

    Chemistry databases

    BindingDBiQ92876.

    Structurei

    Secondary structure

    1244
    Legend: HelixTurnBeta strandPDB Structure known for this area
    Show more details
    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Helixi27 – 29Combined sources3
    Beta strandi36 – 41Combined sources6
    Beta strandi44 – 53Combined sources10
    Beta strandi56 – 59Combined sources4
    Helixi61 – 63Combined sources3
    Beta strandi69 – 73Combined sources5
    Beta strandi75 – 77Combined sources3
    Beta strandi85 – 94Combined sources10
    Turni100 – 102Combined sources3
    Beta strandi108 – 114Combined sources7
    Beta strandi137 – 144Combined sources8
    Beta strandi146 – 149Combined sources4
    Beta strandi156 – 163Combined sources8
    Helixi165 – 171Combined sources7
    Turni173 – 175Combined sources3
    Beta strandi180 – 184Combined sources5
    Turni186 – 188Combined sources3
    Turni194 – 198Combined sources5
    Beta strandi200 – 203Combined sources4
    Beta strandi206 – 213Combined sources8
    Beta strandi221 – 223Combined sources3
    Beta strandi225 – 229Combined sources5
    Helixi230 – 233Combined sources4
    Helixi234 – 237Combined sources4

    3D structure databases

    Select the link destinations:
    PDBei
    RCSB PDBi
    PDBji
    Links Updated
    PDB entryMethodResolution (Å)ChainPositionsPDBsum
    1GVLX-ray1.80A21-243[»]
    1L2EX-ray1.75A22-244[»]
    1LO6X-ray1.56A22-237[»]
    3VFEX-ray1.88A22-244[»]
    4D8NX-ray1.68A22-244[»]
    ProteinModelPortaliQ92876.
    SMRiQ92876.
    ModBaseiSearch...
    MobiDBiSearch...

    Miscellaneous databases

    EvolutionaryTraceiQ92876.

    Family & Domainsi

    Domains and Repeats

    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Domaini22 – 242Peptidase S1PROSITE-ProRule annotationAdd BLAST221

    Sequence similaritiesi

    Belongs to the peptidase S1 family. Kallikrein subfamily.PROSITE-ProRule annotation
    Contains 1 peptidase S1 domain.PROSITE-ProRule annotation

    Keywords - Domaini

    Signal

    Phylogenomic databases

    eggNOGiKOG3627. Eukaryota.
    COG5640. LUCA.
    GeneTreeiENSGT00760000118862.
    HOGENOMiHOG000251820.
    HOVERGENiHBG013304.
    InParanoidiQ92876.
    KOiK08667.
    OMAiAWAEEQN.
    OrthoDBiEOG091G0G5F.
    PhylomeDBiQ92876.
    TreeFamiTF331065.

    Family and domain databases

    CDDicd00190. Tryp_SPc. 1 hit.
    InterProiIPR009003. Peptidase_S1_PA.
    IPR001314. Peptidase_S1A.
    IPR001254. Trypsin_dom.
    IPR018114. TRYPSIN_HIS.
    IPR033116. TRYPSIN_SER.
    [Graphical view]
    PfamiPF00089. Trypsin. 1 hit.
    [Graphical view]
    PRINTSiPR00722. CHYMOTRYPSIN.
    SMARTiSM00020. Tryp_SPc. 1 hit.
    [Graphical view]
    SUPFAMiSSF50494. SSF50494. 1 hit.
    PROSITEiPS50240. TRYPSIN_DOM. 1 hit.
    PS00134. TRYPSIN_HIS. 1 hit.
    PS00135. TRYPSIN_SER. 1 hit.
    [Graphical view]

    Sequences (3)i

    Sequence statusi: Complete.

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

    This entry describes 3 isoformsi produced by alternative splicing. AlignAdd to basket

    Isoform 1 (identifier: Q92876-1) [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
    MKKLMVVLSL IAAAWAEEQN KLVHGGPCDK TSHPYQAALY TSGHLLCGGV
    60 70 80 90 100
    LIHPLWVLTA AHCKKPNLQV FLGKHNLRQR ESSQEQSSVV RAVIHPDYDA
    110 120 130 140 150
    ASHDQDIMLL RLARPAKLSE LIQPLPLERD CSANTTSCHI LGWGKTADGD
    160 170 180 190 200
    FPDTIQCAYI HLVSREECEH AYPGQITQNM LCAGDEKYGK DSCQGDSGGP
    210 220 230 240
    LVCGDHLRGL VSWGNIPCGS KEKPGVYTNV CRYTNWIQKT IQAK
    Length:244
    Mass (Da):26,856
    Last modified:February 1, 1997 - v1
    Checksum:iAEA03F9145D87AAB
    GO
    Isoform 2 (identifier: Q92876-2) [UniParc]FASTAAdd to basket

    The sequence of this isoform differs from the canonical sequence as follows:
         1-107: Missing.

    Show »
    Length:137
    Mass (Da):15,055
    Checksum:i25A421C212869BEA
    GO
    Isoform 3 (identifier: Q92876-3) [UniParc]FASTAAdd to basket

    The sequence of this isoform differs from the canonical sequence as follows:
         14-40: AWAEEQNKLVHGGPCDKTSHPYQAALY → GIFRSSWGSITFGKGRVPRSRVLLSGL
         41-244: Missing.

    Show »
    Length:40
    Mass (Da):4,333
    Checksum:i323721E6AE557378
    GO

    Mass spectrometryi

    Molecular mass is 25866 Da from positions 22 - 244. Determined by MALDI. 1 Publication

    Natural variant

    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Natural variantiVAR_06177678R → W.Corresponds to variant rs61469141dbSNPEnsembl.1

    Alternative sequence

    Feature keyPosition(s)DescriptionActionsGraphical viewLength
    Alternative sequenceiVSP_0344031 – 107Missing in isoform 2. 1 PublicationAdd BLAST107
    Alternative sequenceiVSP_03440414 – 40AWAEE…QAALY → GIFRSSWGSITFGKGRVPRS RVLLSGL in isoform 3. 1 PublicationAdd BLAST27
    Alternative sequenceiVSP_03440541 – 244Missing in isoform 3. 1 PublicationAdd BLAST204

    Sequence databases

    Select the link destinations:
    EMBLi
    GenBanki
    DDBJi
    Links Updated
    U62801 mRNA. Translation: AAB07113.1.
    D78203 mRNA. Translation: BAA11306.1.
    AF013988 mRNA. Translation: AAB66483.1.
    AF149289 Genomic DNA. Translation: AAD51475.1.
    AF243527 Genomic DNA. Translation: AAG33359.1.
    AY318867 mRNA. Translation: AAP82446.1.
    AY318868 mRNA. No translation available.
    AY318869 mRNA. Translation: AAP82448.1.
    AY318870 mRNA. No translation available.
    DQ223012 mRNA. Translation: ABB04464.1.
    AK314897 mRNA. Translation: BAG37411.1.
    BT006852 mRNA. Translation: AAP35498.1.
    AC011483 Genomic DNA. No translation available.
    CH471135 Genomic DNA. Translation: EAW71953.1.
    CH471135 Genomic DNA. Translation: EAW71954.1.
    BC015525 mRNA. Translation: AAH15525.1.
    CCDSiCCDS12811.1. [Q92876-1]
    CCDS42599.1. [Q92876-2]
    RefSeqiNP_001012982.1. NM_001012964.2. [Q92876-1]
    NP_001012983.1. NM_001012965.2. [Q92876-2]
    NP_001306877.1. NM_001319948.1. [Q92876-2]
    NP_001306878.1. NM_001319949.1. [Q92876-2]
    NP_002765.1. NM_002774.3. [Q92876-1]
    UniGeneiHs.79361.

    Genome annotation databases

    EnsembliENST00000310157; ENSP00000309148; ENSG00000167755. [Q92876-1]
    ENST00000376851; ENSP00000366047; ENSG00000167755. [Q92876-1]
    ENST00000391808; ENSP00000375684; ENSG00000167755. [Q92876-2]
    ENST00000594641; ENSP00000470482; ENSG00000167755. [Q92876-1]
    ENST00000597379; ENSP00000469630; ENSG00000167755. [Q92876-3]
    ENST00000599881; ENSP00000471948; ENSG00000167755. [Q92876-3]
    GeneIDi5653.
    KEGGihsa:5653.
    UCSCiuc002pui.4. human. [Q92876-1]

    Keywords - Coding sequence diversityi

    Alternative splicing, Polymorphism

    Cross-referencesi

    Sequence databases

    Select the link destinations:
    EMBLi
    GenBanki
    DDBJi
    Links Updated
    U62801 mRNA. Translation: AAB07113.1.
    D78203 mRNA. Translation: BAA11306.1.
    AF013988 mRNA. Translation: AAB66483.1.
    AF149289 Genomic DNA. Translation: AAD51475.1.
    AF243527 Genomic DNA. Translation: AAG33359.1.
    AY318867 mRNA. Translation: AAP82446.1.
    AY318868 mRNA. No translation available.
    AY318869 mRNA. Translation: AAP82448.1.
    AY318870 mRNA. No translation available.
    DQ223012 mRNA. Translation: ABB04464.1.
    AK314897 mRNA. Translation: BAG37411.1.
    BT006852 mRNA. Translation: AAP35498.1.
    AC011483 Genomic DNA. No translation available.
    CH471135 Genomic DNA. Translation: EAW71953.1.
    CH471135 Genomic DNA. Translation: EAW71954.1.
    BC015525 mRNA. Translation: AAH15525.1.
    CCDSiCCDS12811.1. [Q92876-1]
    CCDS42599.1. [Q92876-2]
    RefSeqiNP_001012982.1. NM_001012964.2. [Q92876-1]
    NP_001012983.1. NM_001012965.2. [Q92876-2]
    NP_001306877.1. NM_001319948.1. [Q92876-2]
    NP_001306878.1. NM_001319949.1. [Q92876-2]
    NP_002765.1. NM_002774.3. [Q92876-1]
    UniGeneiHs.79361.

    3D structure databases

    Select the link destinations:
    PDBei
    RCSB PDBi
    PDBji
    Links Updated
    PDB entryMethodResolution (Å)ChainPositionsPDBsum
    1GVLX-ray1.80A21-243[»]
    1L2EX-ray1.75A22-244[»]
    1LO6X-ray1.56A22-237[»]
    3VFEX-ray1.88A22-244[»]
    4D8NX-ray1.68A22-244[»]
    ProteinModelPortaliQ92876.
    SMRiQ92876.
    ModBaseiSearch...
    MobiDBiSearch...

    Protein-protein interaction databases

    BioGridi111634. 12 interactors.
    IntActiQ92876. 16 interactors.
    STRINGi9606.ENSP00000309148.

    Chemistry databases

    BindingDBiQ92876.
    ChEMBLiCHEMBL4448.
    GuidetoPHARMACOLOGYi2376.

    Protein family/group databases

    MEROPSiS01.236.

    PTM databases

    PhosphoSitePlusiQ92876.
    UniCarbKBiQ92876.

    Polymorphism and mutation databases

    BioMutaiKLK6.
    DMDMi3914480.

    Proteomic databases

    MaxQBiQ92876.
    PaxDbiQ92876.
    PeptideAtlasiQ92876.
    PRIDEiQ92876.

    Protocols and materials databases

    DNASUi5653.
    Structural Biology KnowledgebaseSearch...

    Genome annotation databases

    EnsembliENST00000310157; ENSP00000309148; ENSG00000167755. [Q92876-1]
    ENST00000376851; ENSP00000366047; ENSG00000167755. [Q92876-1]
    ENST00000391808; ENSP00000375684; ENSG00000167755. [Q92876-2]
    ENST00000594641; ENSP00000470482; ENSG00000167755. [Q92876-1]
    ENST00000597379; ENSP00000469630; ENSG00000167755. [Q92876-3]
    ENST00000599881; ENSP00000471948; ENSG00000167755. [Q92876-3]
    GeneIDi5653.
    KEGGihsa:5653.
    UCSCiuc002pui.4. human. [Q92876-1]

    Organism-specific databases

    CTDi5653.
    DisGeNETi5653.
    GeneCardsiKLK6.
    HGNCiHGNC:6367. KLK6.
    HPAiHPA051837.
    MIMi602652. gene.
    neXtProtiNX_Q92876.
    OpenTargetsiENSG00000167755.
    PharmGKBiPA30156.
    GenAtlasiSearch...

    Phylogenomic databases

    eggNOGiKOG3627. Eukaryota.
    COG5640. LUCA.
    GeneTreeiENSGT00760000118862.
    HOGENOMiHOG000251820.
    HOVERGENiHBG013304.
    InParanoidiQ92876.
    KOiK08667.
    OMAiAWAEEQN.
    OrthoDBiEOG091G0G5F.
    PhylomeDBiQ92876.
    TreeFamiTF331065.

    Enzyme and pathway databases

    BioCyciZFISH:ENSG00000167755-MONOMER.
    BRENDAi3.4.21.104. 2681.
    3.4.21.34. 2681.
    3.4.21.B10. 2681.
    SABIO-RKQ92876.

    Miscellaneous databases

    ChiTaRSiKLK6. human.
    EvolutionaryTraceiQ92876.
    GeneWikiiKLK6.
    GenomeRNAii5653.
    PMAP-CutDBQ92876.
    PROiQ92876.
    SOURCEiSearch...

    Gene expression databases

    BgeeiENSG00000167755.
    CleanExiHS_KLK6.
    ExpressionAtlasiQ92876. baseline and differential.
    GenevisibleiQ92876. HS.

    Family and domain databases

    CDDicd00190. Tryp_SPc. 1 hit.
    InterProiIPR009003. Peptidase_S1_PA.
    IPR001314. Peptidase_S1A.
    IPR001254. Trypsin_dom.
    IPR018114. TRYPSIN_HIS.
    IPR033116. TRYPSIN_SER.
    [Graphical view]
    PfamiPF00089. Trypsin. 1 hit.
    [Graphical view]
    PRINTSiPR00722. CHYMOTRYPSIN.
    SMARTiSM00020. Tryp_SPc. 1 hit.
    [Graphical view]
    SUPFAMiSSF50494. SSF50494. 1 hit.
    PROSITEiPS50240. TRYPSIN_DOM. 1 hit.
    PS00134. TRYPSIN_HIS. 1 hit.
    PS00135. TRYPSIN_SER. 1 hit.
    [Graphical view]
    ProtoNetiSearch...

    Entry informationi

    Entry nameiKLK6_HUMAN
    AccessioniPrimary (citable) accession number: Q92876
    Secondary accession number(s): A6NJA1, A8MW09, Q6H301
    Entry historyi
    Integrated into UniProtKB/Swiss-Prot: December 15, 1998
    Last sequence update: February 1, 1997
    Last modified: November 2, 2016
    This is version 153 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 19
      Human chromosome 19: 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. Peptidase families
      Classification of peptidase families and list of entries
    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.