Seroatlas · Human Serome Atlas

XK

Endoplasmic reticulum membrane adapter protein XK

Also known as: Kx, NAC, X1k, XK_HUMAN, XKR1

Cross-references: UniProt · Ensembl · Human Protein Atlas · GeneCards · NCBI Gene

Protein identityUniProt · HPA

UniProt accession
P51811
Gene
XK
Ensembl
ENSG00000047597
Chromosome
X
Canonical length
444 aa
Protein class
Blood group antigen proteins, Disease related genes, Human disease related genes, Potential drug targets, Predicted membrane proteins, Transporters
Subcellular location
Nucleoplasm,Vesicles,Mitochondria

OverviewNCBI Gene

This locus controls the synthesis of the Kell blood group 'precursor substance' (Kx). Mutations in this gene have been associated with McLeod syndrome, an X-linked, recessive disorder characterized by abnormalities in the neuromuscular and hematopoietic systems. The encoded protein has structural characteristics of prokaryotic and eukaryotic membrane transport proteins. [provided by RefSeq, Jul 2008]

Canonical amino-acid sequenceUniProt

444 residues, UniProt reviewed canonical sequence.

>P51811|XK
     1  MKFPASVLAS VFLFVAETTA ALSLSSTYRS GGDRMWQALT LLFSLLPCAL VQLTLLFVHR
    61  DLSRDRPLVL LLHLLQLGPL FRCFEVFCIY FQSGNNEEPY VSITKKRQMP KNGLSEEIEK
   121  EVGQAEGKLI THRSAFSRAS VIQAFLGSAP QLTLQLYISV MQQDVTVGRS LLMTISLLSI
   181  VYGALRCNIL AIKIKYDEYE VKVKPLAYVC IFLWRSFEIA TRVVVLVLFT SVLKTWVVVI
   241  ILINFFSFFL YPWILFWCSG SPFPENIEKA LSRVGTTIVL CFLTLLYTGI NMFCWSAVQL
   301  KIDSPDLISK SHNWYQLLVY YMIRFIENAI LLLLWYLFKT DIYMYVCAPL LVLQLLIGYC
   361  TAILFMLVFY QFFHPCKKLF SSSVSEGFQR WLRCFCWACR QQKPCEPIGK EDLQSSRDRD
   421  ETPSSSKTSP EPGQFLNAED LCSA

LocalizationUniProt · AlphaFold · HPA

Whether an antibody against XK can act on the native protein depends on physical access: surface and secreted proteins are reachable by circulating antibodies, intracellular proteins usually are not.

Antibody reachability
Other membrane
Secreted
No
Transmembrane segments
10
Mean surface accessibility (rSASA)
0.32
Highest tissue expression
13 nTPM

Expression across tissuesHPA

Tissue

  • bone marrow: 13 nTPM
  • colon: 11 nTPM
  • stomach: 11 nTPM
  • rectum: 11 nTPM
  • duodenum: 10 nTPM
  • small intestine: 9.9 nTPM

Single-cell type

  • platelets: 247 nCPM
  • erythrocyte progenitors: 65 nCPM
  • foveolar cells: 48 nCPM
  • megakaryocytes: 43 nCPM
  • megakaryocyte progenitors: 37 nCPM
  • gastric chief cells: 33 nCPM

Immune cell

  • basophil: 10 nTPM
  • eosinophil: 5.8 nTPM
  • total PBMC: 0.4 nTPM
  • neutrophil: 0.1 nTPM
  • classical monocyte: 0 nTPM
  • gdT-cell: 0 nTPM

Brain region

  • hypothalamus: 15 nTPM
  • cerebral cortex: 9.9 nTPM
  • basal ganglia: 8.5 nTPM
  • cerebellum: 8.3 nTPM
  • pons: 7.6 nTPM
  • medulla oblongata: 6.8 nTPM

DiseaseUniProt · ClinVar · IEDB · PubMed

Four sources answering four different questions about XK.

Disease | AllUniProt

Conditions XK is implicated in, by any mechanism.

Disease | GeneticClinVar

15 pathogenic / likely-pathogenic of 135 ClinVar records.

Conditions with pathogenic or likely-pathogenic variants.

Genetic constraint and essentialitygnomAD · DepMap

Does the body need this protein intact? Low LOEUF or a strong DepMap dependency means loss or blockade of the protein is likely to be felt.

gnomAD LOEUF (loss-of-function intolerance)
0.31
gnomAD pLI
0.95
gnomAD missense Z
2.12
DepMap mean gene effect
0.08
DepMap dependency class
none

Cancer expressionTCGA

Across TCGA tumor cohorts, this protein is over-expressed in roughly 6% of surveyed tumor types (aggregate summary; per-cohort expression, alteration, and survival load in the interactive view).

OntologyGO

Biological processes

Molecular functions

Cellular components

Protein domainsUniProt · Pfam · InterPro

KeywordsUniProt

InteractionsUniProt · HPA

Protein binding partners of XK in the human serome: UniProt-annotated complex subunits plus reported interactors. Each links to its own Seroatlas record.

Antibody and autoantibody relevanceSeroatlas analysis

Seroatlas reads XK as an antibody target. Whether an autoantibody or antibody against XK could matter depends on whether native XK is physically reachable, whether the body needs it intact, and whether it acts in a disease-relevant tissue.

XK is annotated as predominantly intracellular. Intracellular proteins are common autoantibody markers, becoming visible to the immune system after cell injury or altered processing, but are usually markers of disease rather than direct drivers.

Annotation status

The present source text does not explicitly label XK as an autoantigen. Seroatlas presents hypothesis context only and does not manufacture a known-serology claim.

Canonical record: https://seroatlas.com/gene/XK. Study-independent annotations aggregated from UniProt, Human Protein Atlas, PubMed, IEDB, Pfam, InterPro, Gene Ontology, AlphaFold, gnomAD, DepMap, ClinVar, TCGA. Catalog release seroatlas-reviewed-human-uniprot-20260313.

Seroatlas is the reference for exploring autoantibody and antibody serology at the human-protein level: the autoreactome and human serome, multiplex serology (HuProt, HuScan, VirScan, PhIP-Seq).

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