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Protein

Hexokinase-1

Gene

Hk1

Organism
Mus musculus (Mouse)
Status
Reviewed-Annotation score: Annotation score: 5 out of 5-Experimental evidence at protein leveli

Functioni

Catalytic activityi

ATP + D-hexose = ADP + D-hexose 6-phosphate.

Enzyme regulationi

Hexokinase is an allosteric enzyme inhibited by its product Glc-6-P.

Pathwayi

Sites

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Binding sitei86 – 861ATP 1By similarity
Binding sitei211 – 2111Substrate 1By similarity
Binding sitei265 – 2651Glucose-6-phosphate 1By similarity
Binding sitei288 – 2881Glucose-6-phosphate 1By similarity
Binding sitei291 – 2911Substrate 1By similarity
Binding sitei316 – 3161Substrate 1By similarity
Binding sitei505 – 5051Glucose-6-phosphate 1By similarity
Binding sitei659 – 6591Glucose-6-phosphate 2By similarity
Binding sitei713 – 7131Glucose-6-phosphate 2By similarity
Binding sitei736 – 7361ATP 2By similarity
Binding sitei736 – 7361Glucose-6-phosphate 2By similarity
Binding sitei739 – 7391Substrate 2By similarity
Binding sitei764 – 7641Substrate 2By similarity
Binding sitei798 – 7981Substrate 2By similarity
Binding sitei953 – 9531Glucose-6-phosphate 2By similarity

Regions

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Nucleotide bindingi140 – 1456ATP 1Sequence Analysis
Nucleotide bindingi481 – 4822ATP 1By similarity
Nucleotide bindingi588 – 5936ATP 2By similarity
Nucleotide bindingi803 – 8042ATP 2By similarity
Nucleotide bindingi840 – 8445ATP 2By similarity
Nucleotide bindingi919 – 9235ATP 2By similarity

GO - Molecular functioni

  • ATP binding Source: UniProtKB-KW
  • fructokinase activity Source: GO_Central
  • glucokinase activity Source: MGI
  • hexokinase activity Source: MGI
  • mannokinase activity Source: GO_Central

GO - Biological processi

  • canonical glycolysis Source: MGI
  • carbohydrate phosphorylation Source: GOC
  • cellular glucose homeostasis Source: GO_Central
  • glucose 6-phosphate metabolic process Source: GOC
  • glycolytic process Source: MGI
Complete GO annotation...

Keywords - Molecular functioni

Kinase, Transferase

Keywords - Biological processi

Glycolysis

Keywords - Ligandi

ATP-binding, Nucleotide-binding

Enzyme and pathway databases

ReactomeiREACT_297294. Glucose transport.
REACT_314687. Glycolysis.
SABIO-RKP17710.
UniPathwayiUPA00242.

Names & Taxonomyi

Protein namesi
Recommended name:
Hexokinase-1 (EC:2.7.1.1)
Alternative name(s):
Hexokinase type I
Short name:
HK I
Hexokinase, tumor isozyme
Gene namesi
Name:Hk1
OrganismiMus musculus (Mouse)
Taxonomic identifieri10090 [NCBI]
Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresGliresRodentiaSciurognathiMuroideaMuridaeMurinaeMusMus
ProteomesiUP000000589 Componenti: Chromosome 10

Organism-specific databases

MGIiMGI:96103. Hk1.

Subcellular locationi

Isoform HK1-SC :

GO - Cellular componenti

  • cilium Source: MGI
  • cytosol Source: MGI
  • membrane raft Source: MGI
  • mitochondrial outer membrane Source: UniProtKB-SubCell
  • mitochondrion Source: MGI
  • sperm principal piece Source: MGI
Complete GO annotation...

Keywords - Cellular componenti

Membrane, Mitochondrion, Mitochondrion outer membrane

Pathology & Biotechi

Mutagenesis

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Mutagenesisi67 – 671P → A: Disrupts targeting to membrane; when associated with N-68; Q-70; P-73; A-74 and Q-75. 1 Publication
Mutagenesisi68 – 681K → N: Disrupts targeting to membrane; when associated with A-67; Q-70; P-73; A-74 and Q-75. 1 Publication
Mutagenesisi70 – 701R → Q: Disrupts targeting to membrane; when associated with A-67; N-68; P-73; A-74 and Q-75. 1 Publication
Mutagenesisi73 – 731L → P: Disrupts targeting to membrane; when associated with A-67; N-68; Q-70; A-74 and Q-75. 1 Publication
Mutagenesisi74 – 741T → A: Disrupts targeting to membrane; when associated with A-67; N-68; Q-70; P-73 and Q-75. 1 Publication
Mutagenesisi75 – 751E → Q: Disrupts targeting to membrane; when associated with A-67; N-68; Q-70; P-73 and A-74. 1 Publication

PTM / Processingi

Molecule processing

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Chaini1 – 974974Hexokinase-1PRO_0000013399Add
BLAST

Post-translational modificationi

Isoform HK1-SC is tyrosine-phosphorylated.1 Publication

Keywords - PTMi

Phosphoprotein

Proteomic databases

MaxQBiP17710.
PaxDbiP17710.
PRIDEiP17710.

PTM databases

PhosphoSiteiP17710.

Expressioni

Tissue specificityi

In rapidly growing tumor cells exhibiting high glucose catabolic rates, isoform HK1 is markedly elevated. Isoform HK1-SA, isoform HK1-SB and isoform HK1-SC are found only in spermatogenic cells. Isoform HK1-SC is detected in round spermatids, condensing spermatids and mature sperm where it is found in the head membranes, mitochondria of the midpiece and the fibrous sheath of the flagellum. Expressed within the principal piece and midpiece of sperm tail (at protein level).1 Publication

Developmental stagei

Isoform HK1-SA is first expressed during meiosis and continues to be present in postmeiotic germ cells while isoform HK1-SB is present only in postmeiotic germ cells.2 Publications

Gene expression databases

BgeeiP17710.
CleanExiMM_HK1.
ExpressionAtlasiP17710. baseline and differential.
GenevestigatoriP17710.

Interactioni

Subunit structurei

Monomer. Interacts with VDAC1. The HK1-VDAC1 complex interacts with ATF2 (By similarity). Interacts with RABL2/RABL2A; binds preferentially to GTP-bound RABL2. Interacts (via N-terminal spermatogenic cell-specific region) with PFKM isoform 2 and isoform 3 (via C-terminus) (PubMed:19889946).By similarity2 Publications

Protein-protein interaction databases

IntActiP17710. 6 interactions.
MINTiMINT-1847872.

Structurei

3D structure databases

ProteinModelPortaliP17710.
SMRiP17710. Positions 76-967.
ModBaseiSearch...
MobiDBiSearch...

Family & Domainsi

Domains and Repeats

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Domaini72 – 514443Hexokinase 1PROSITE-ProRule annotationAdd
BLAST
Domaini520 – 962443Hexokinase 2PROSITE-ProRule annotationAdd
BLAST

Region

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Regioni1 – 5252HydrophobicAdd
BLAST
Regioni53 – 531479RegulatoryAdd
BLAST
Regioni129 – 263135Hexokinase small subdomain 1PROSITE-ProRule annotationAdd
BLAST
Regioni140 – 1445Glucose-6-phosphate 1 bindingBy similarity
Regioni228 – 2292Substrate 1 bindingBy similarity
Regioni264 – 503240Hexokinase large subdomain 1PROSITE-ProRule annotationAdd
BLAST
Regioni264 – 2652Substrate 1 bindingBy similarity
Regioni347 – 3504Substrate 1 bindingBy similarity
Regioni469 – 4713Glucose-6-phosphate 1 bindingBy similarity
Regioni532 – 974443CatalyticAdd
BLAST
Regioni577 – 711135Hexokinase small subdomain 2PROSITE-ProRule annotationAdd
BLAST
Regioni588 – 5925Glucose-6-phosphate 2 bindingBy similarity
Regioni659 – 6602Substrate 2 bindingBy similarity
Regioni676 – 6772Substrate 2 bindingBy similarity
Regioni712 – 951240Hexokinase large subdomain 2PROSITE-ProRule annotationAdd
BLAST
Regioni712 – 7132Substrate 2 bindingBy similarity
Regioni917 – 9193Glucose-6-phosphate 2 bindingBy similarity

Domaini

The N- and C-terminal halves of this hexokinase show extensive sequence similarity to each other. The catalytic activity is associated with the C-terminus while regulatory function is associated with the N-terminus. Each domain can bind a single glucose and Gluc-6-P molecule (By similarity).By similarity

Sequence similaritiesi

Belongs to the hexokinase family.PROSITE-ProRule annotationCurated
Contains 2 hexokinase domains.PROSITE-ProRule annotation

Keywords - Domaini

Repeat

Phylogenomic databases

eggNOGiCOG5026.
GeneTreeiENSGT00390000017159.
HOGENOMiHOG000162671.
HOVERGENiHBG005020.
InParanoidiP17710.
KOiK00844.
OMAiKFKASGV.
OrthoDBiEOG7S21X5.
TreeFamiTF314238.

Family and domain databases

InterProiIPR001312. Hexokinase.
IPR022673. Hexokinase_C.
IPR019807. Hexokinase_CS.
IPR022672. Hexokinase_N.
[Graphical view]
PANTHERiPTHR19443. PTHR19443. 1 hit.
PfamiPF00349. Hexokinase_1. 2 hits.
PF03727. Hexokinase_2. 2 hits.
[Graphical view]
PRINTSiPR00475. HEXOKINASE.
PROSITEiPS00378. HEXOKINASE_1. 2 hits.
PS51748. HEXOKINASE_2. 2 hits.
[Graphical view]

Sequences (4)i

Sequence statusi: Complete.

This entry describes 4 isoformsi produced by alternative splicing and alternative initiation. AlignAdd to basket

Isoform HK1-SA (identifier: P17710-1) [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
MGWGAPLLSR MLHGPGQAGE TSPVPERQSG SENPASEDRR PLEKQCSHHL
60 70 80 90 100
YTMGQNCQRG QAVDVEPKIR PPLTEEKIDK YLYAMRLSDE ILIDILTRFK
110 120 130 140 150
KEMKNGLSRD YNPTASVKML PTFVRSIPDG SEKGDFIALD LGGSSFRILR
160 170 180 190 200
VQVNHEKSQN VSMESEVYDT PENIVHGSGS QLFDHVAECL GDFMEKRKIK
210 220 230 240 250
DKKLPVGFTF SFPCRQSKID EAVLITWTKR FKASGVEGAD VVKLLNKAIK
260 270 280 290 300
KRGDYDANIV AVVNDTVGTM MTCGYDDQQC EVGLIIGTGT NACYMEELRH
310 320 330 340 350
IDLVEGDEGR MCINTEWGAF GDDGSLEDIR TEFDRELDRG SLNPGKQLFE
360 370 380 390 400
KMVSGMYMGE LVRLILVKMA KESLLFEGRI TPELLTRGKF TTSDVAAIET
410 420 430 440 450
DKEGVQNAKE ILTRLGVEPS HDDCVSVQHV CTIVSFRSAN LVAATLGAIL
460 470 480 490 500
NRLRDNKGTP RLRTTVGVDG SLYKMHPQYS RRFHKTLRRL VPDSDVRFLL
510 520 530 540 550
SESGSGKGAA MVTAVAYRLA EQHRQIEETL SHFRLSKQAL MEVKKKLRSE
560 570 580 590 600
MEMGLRKETN SRATVKMLPS YVRSIPDGTE HGDFLALDLG GTNFRVLLVK
610 620 630 640 650
IRSGKKRTVE MHNKIYSIPL EIMQGTGDEL FDHIVSCISD FLDYMGIKGP
660 670 680 690 700
RMPLGFTFSF PCKQTSLDCG ILITWTKGFK ATDCVGHDVA TLLRDAVKRR
710 720 730 740 750
EEFDLDVVAV VNDTVGTMMT CAYEEPSCEI GLIVGTGSNA CYMEEMKNVE
760 770 780 790 800
MVEGNQGQMC INMEWGAFGD NGCLDDIRTD FDKVVDEYSL NSGKQRFEKM
810 820 830 840 850
ISGMYLGEIV RNILIDFTKK GFLFRGQISE PLKTRGIFET KFLSQIESDR
860 870 880 890 900
LALLQVRAIL QQLGLNSTCD DSILVKTVCG VVSKRAAQLC GAGMAAVVEK
910 920 930 940 950
IRENRGLDHL NVTVGVDGTL YKLHPHFSRI MHQTVKELSP KCTVSFLLSE
960 970
DGSGKGAALI TAVGVRLRGD PTNA
Length:974
Mass (Da):108,303
Last modified:July 27, 2011 - v3
Checksum:i6122505622F7BA3D
GO
Isoform HK1-SB (identifier: P17710-2) [UniParc]FASTAAdd to basket

The sequence of this isoform differs from the canonical sequence as follows:
     1-52: Missing.
     400-400: T → TGWELSPDRRWYQAYMRCTQDTHR

Note: Produced by alternative splicing and alternative initiation at Met-53 of isoform HK1-SA.

Show »
Length:945
Mass (Da):105,575
Checksum:i770DED5C144B9DE7
GO
Isoform HK1 (identifier: P17710-3) [UniParc]FASTAAdd to basket

The sequence of this isoform differs from the canonical sequence as follows:
     1-76: MGWGAPLLSR...PKIRPPLTEE → MIAAQLLAYYFTELKDDQVK

Show »
Length:918
Mass (Da):102,302
Checksum:i4F0E6923F1EEC9B5
GO
Isoform HK1-SC (identifier: P17710-4) [UniParc]FASTAAdd to basket

The sequence of this isoform differs from the canonical sequence as follows:
     1-52: Missing.

Note: Produced by alternative initiation at Met-53 of isoform HK1-SA.

Show »
Length:922
Mass (Da):102,637
Checksum:i4449779BF37D6EB7
GO

Experimental Info

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Sequence conflicti870 – 8701D → S in AAA37804 (PubMed:2318862).Curated
Sequence conflicti899 – 8991E → Q in AAB57759 (PubMed:8396993).Curated

Alternative sequence

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Alternative sequencei1 – 7676MGWGA…PLTEE → MIAAQLLAYYFTELKDDQVK in isoform HK1. 1 PublicationVSP_007327Add
BLAST
Alternative sequencei1 – 5252Missing in isoform HK1-SB and isoform HK1-SC. 1 PublicationVSP_018747Add
BLAST
Alternative sequencei400 – 4001T → TGWELSPDRRWYQAYMRCTQ DTHR in isoform HK1-SB. 1 PublicationVSP_007328

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
J05277 mRNA. Translation: AAA37804.1.
L16948 mRNA. Translation: AAB57760.1.
L16949 mRNA. Translation: AAB57759.1.
L16950 mRNA. Translation: AAA53036.1.
AC126428 Genomic DNA. No translation available.
AC145297 Genomic DNA. No translation available.
CCDSiCCDS48577.1. [P17710-3]
CCDS48578.1. [P17710-2]
PIRiA35244.
I49744.
RefSeqiXP_006513305.1. XM_006513242.1. [P17710-1]
XP_006513306.1. XM_006513243.2. [P17710-4]
XP_006513307.1. XM_006513244.2. [P17710-4]
XP_006513308.1. XM_006513245.2. [P17710-4]
UniGeneiMm.196605.

Genome annotation databases

EnsembliENSMUST00000072357; ENSMUSP00000072195; ENSMUSG00000037012. [P17710-2]
ENSMUST00000099691; ENSMUSP00000097282; ENSMUSG00000037012. [P17710-3]
ENSMUST00000116238; ENSMUSP00000111946; ENSMUSG00000037012. [P17710-2]
GeneIDi15275.
KEGGimmu:15275.
UCSCiuc007fgz.2. mouse. [P17710-2]

Keywords - Coding sequence diversityi

Alternative initiation, Alternative splicing

Cross-referencesi

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
J05277 mRNA. Translation: AAA37804.1.
L16948 mRNA. Translation: AAB57760.1.
L16949 mRNA. Translation: AAB57759.1.
L16950 mRNA. Translation: AAA53036.1.
AC126428 Genomic DNA. No translation available.
AC145297 Genomic DNA. No translation available.
CCDSiCCDS48577.1. [P17710-3]
CCDS48578.1. [P17710-2]
PIRiA35244.
I49744.
RefSeqiXP_006513305.1. XM_006513242.1. [P17710-1]
XP_006513306.1. XM_006513243.2. [P17710-4]
XP_006513307.1. XM_006513244.2. [P17710-4]
XP_006513308.1. XM_006513245.2. [P17710-4]
UniGeneiMm.196605.

3D structure databases

ProteinModelPortaliP17710.
SMRiP17710. Positions 76-967.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

IntActiP17710. 6 interactions.
MINTiMINT-1847872.

PTM databases

PhosphoSiteiP17710.

Proteomic databases

MaxQBiP17710.
PaxDbiP17710.
PRIDEiP17710.

Protocols and materials databases

Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsembliENSMUST00000072357; ENSMUSP00000072195; ENSMUSG00000037012. [P17710-2]
ENSMUST00000099691; ENSMUSP00000097282; ENSMUSG00000037012. [P17710-3]
ENSMUST00000116238; ENSMUSP00000111946; ENSMUSG00000037012. [P17710-2]
GeneIDi15275.
KEGGimmu:15275.
UCSCiuc007fgz.2. mouse. [P17710-2]

Organism-specific databases

CTDi3098.
MGIiMGI:96103. Hk1.

Phylogenomic databases

eggNOGiCOG5026.
GeneTreeiENSGT00390000017159.
HOGENOMiHOG000162671.
HOVERGENiHBG005020.
InParanoidiP17710.
KOiK00844.
OMAiKFKASGV.
OrthoDBiEOG7S21X5.
TreeFamiTF314238.

Enzyme and pathway databases

UniPathwayiUPA00242.
ReactomeiREACT_297294. Glucose transport.
REACT_314687. Glycolysis.
SABIO-RKP17710.

Miscellaneous databases

PROiP17710.
SOURCEiSearch...

Gene expression databases

BgeeiP17710.
CleanExiMM_HK1.
ExpressionAtlasiP17710. baseline and differential.
GenevestigatoriP17710.

Family and domain databases

InterProiIPR001312. Hexokinase.
IPR022673. Hexokinase_C.
IPR019807. Hexokinase_CS.
IPR022672. Hexokinase_N.
[Graphical view]
PANTHERiPTHR19443. PTHR19443. 1 hit.
PfamiPF00349. Hexokinase_1. 2 hits.
PF03727. Hexokinase_2. 2 hits.
[Graphical view]
PRINTSiPR00475. HEXOKINASE.
PROSITEiPS00378. HEXOKINASE_1. 2 hits.
PS51748. HEXOKINASE_2. 2 hits.
[Graphical view]
ProtoNetiSearch...

Publicationsi

« Hide 'large scale' publications
  1. "Glucose phosphorylation in tumor cells. Cloning, sequencing, and overexpression in active form of a full-length cDNA encoding a mitochondrial bindable form of hexokinase."
    Arora K.K., Fanciulli M., Pedersen P.L.
    J. Biol. Chem. 265:6481-6488(1990) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA] (ISOFORM HK1).
  2. "Unique hexokinase messenger ribonucleic acids lacking the porin-binding domain are developmentally expressed in mouse spermatogenic cells."
    Mori C., Welch J.E., Fulcher K.D., O'Brien D.A., Eddy E.M.
    Biol. Reprod. 49:191-203(1993) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA] (ISOFORMS HK1-SA; HK1-SB AND HK1-SC), DEVELOPMENTAL STAGE.
    Strain: CD-1.
    Tissue: Testis.
  3. Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
    Strain: C57BL/6J.
  4. Lubec G., Kang S.U.
    Submitted (APR-2007) to UniProtKB
    Strain: C57BL/6.
    Tissue: Brain.
  5. "Targeting of a germ cell-specific type 1 hexokinase lacking a porin-binding domain to the mitochondria as well as to the head and fibrous sheath of murine spermatozoa."
    Travis A.J., Foster J.A., Rosenbaum N.A., Visconti P.E., Gerton G.L., Kopf G.S., Moss S.B.
    Mol. Biol. Cell 9:263-276(1998) [PubMed] [Europe PMC] [Abstract]
    Cited for: SUBCELLULAR LOCATION, DEVELOPMENTAL STAGE, PHOSPHORYLATION.
  6. "A novel NH(2)-terminal, nonhydrophobic motif targets a male germ cell-specific hexokinase to the endoplasmic reticulum and plasma membrane."
    Travis A.J., Sui D., Riedel K.D., Hofmann N.R., Moss S.B., Wilson J.E., Kopf G.S.
    J. Biol. Chem. 274:34467-34475(1999) [PubMed] [Europe PMC] [Abstract]
    Cited for: MUTAGENESIS OF PRO-67; LYS-68; ARG-70; LEU-73; THR-74 AND GLU-75.
  7. "Molecular complex of three testis-specific isozymes associated with the mouse sperm fibrous sheath: hexokinase 1, phosphofructokinase M, and glutathione S-transferase mu class 5."
    Nakamura N., Mori C., Eddy E.M.
    Biol. Reprod. 82:504-515(2010) [PubMed] [Europe PMC] [Abstract]
    Cited for: INTERACTION WITH PFKM.
  8. "RAB-like 2 has an essential role in male fertility, sperm intra-flagellar transport, and tail assembly."
    Lo J.C., Jamsai D., O'Connor A.E., Borg C., Clark B.J., Whisstock J.C., Field M.C., Adams V., Ishikawa T., Aitken R.J., Whittle B., Goodnow C.C., Ormandy C.J., O'Bryan M.K.
    PLoS Genet. 8:E1002969-E1002969(2012) [PubMed] [Europe PMC] [Abstract]
    Cited for: INTERACTION WITH RABL2, TISSUE SPECIFICITY.

Entry informationi

Entry nameiHXK1_MOUSE
AccessioniPrimary (citable) accession number: P17710
Secondary accession number(s): E9PXQ3
, Q61659, Q64476, Q64479
Entry historyi
Integrated into UniProtKB/Swiss-Prot: August 1, 1990
Last sequence update: July 27, 2011
Last modified: May 27, 2015
This is version 154 of the entry and version 3 of the sequence. [Complete history]
Entry statusiReviewed (UniProtKB/Swiss-Prot)
Annotation programChordata Protein Annotation Program

Miscellaneousi

Miscellaneous

In vertebrates there are four major glucose-phosphorylating isoenzymes, designated hexokinase I, II, III and IV (glucokinase).

Keywords - Technical termi

Allosteric enzyme, Complete proteome, Direct protein sequencing, Reference proteome

Documents

  1. MGD cross-references
    Mouse Genome Database (MGD) cross-references in UniProtKB/Swiss-Prot
  2. PATHWAY comments
    Index of metabolic and biosynthesis pathways
  3. 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.