Seroatlas · Human Serome Atlas

CTSK

Cathepsin K

Also known as: CATK_HUMAN, CTSO, CTSO2, PKND, PYCD

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

Protein identityUniProt · HPA

UniProt accession
P43235
Gene
CTSK
Ensembl
ENSG00000143387
Chromosome
1
Canonical length
329 aa
Protein class
Disease related genes, Enzymes, Human disease related genes, Metabolic proteins, Plasma proteins, Potential drug targets, Predicted intracellular proteins, Predicted membrane proteins
Subcellular location
Vesicles
Secretome location
Intracellular and membrane

OverviewNCBI Gene

The protein encoded by this gene is a lysosomal cysteine proteinase involved in bone remodeling and resorption. This protein, which is a member of the peptidase C1 protein family, is predominantly expressed in osteoclasts. However, the encoded protein is also expressed in a significant fraction of human breast cancers, where it could contribute to tumor invasiveness. Mutations in this gene are the cause of pycnodysostosis, an autosomal recessive disease characterized by osteosclerosis and short stature. [provided by RefSeq, Apr 2013]

Canonical amino-acid sequenceUniProt

329 residues, UniProt reviewed canonical sequence.

>P43235|CTSK
     1  MWGLKVLLLP VVSFALYPEE ILDTHWELWK KTHRKQYNNK VDEISRRLIW EKNLKYISIH
    61  NLEASLGVHT YELAMNHLGD MTSEEVVQKM TGLKVPLSHS RSNDTLYIPE WEGRAPDSVD
   121  YRKKGYVTPV KNQGQCGSCW AFSSVGALEG QLKKKTGKLL NLSPQNLVDC VSENDGCGGG
   181  YMTNAFQYVQ KNRGIDSEDA YPYVGQEESC MYNPTGKAAK CRGYREIPEG NEKALKRAVA
   241  RVGPVSVAID ASLTSFQFYS KGVYYDESCN SDNLNHAVLA VGYGIQKGNK HWIIKNSWGE
   301  NWGNKGYILM ARNKNNACGI ANLASFPKM

LocalizationUniProt · AlphaFold · HPA

Whether an antibody against CTSK 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
Cell surface
Secreted
No
Transmembrane segments
0
Mean surface accessibility (rSASA)
0.26
Highest tissue expression
334 nTPM

Expression across tissuesHPA

Tissue

  • cervix: 334 nTPM
  • gallbladder: 280 nTPM
  • endometrium: 221 nTPM
  • breast: 214 nTPM
  • adipose tissue: 207 nTPM
  • urinary bladder: 197 nTPM

Single-cell type

  • fibroblasts: 348 nCPM
  • decidual stromal cells: 334 nCPM
  • retinal pigment epithelial cells: 239 nCPM
  • peritubular myoid cells: 136 nCPM
  • melanocytes: 95 nCPM
  • leydig cells: 94 nCPM

Immune cell

  • classical monocyte: 1.9 nTPM
  • intermediate monocyte: 1 nTPM
  • total PBMC: 0.6 nTPM
  • T-reg: 0.4 nTPM
  • non-classical monocyte: 0.3 nTPM
  • eosinophil: 0.2 nTPM

Brain region

  • choroid plexus: 31 nTPM
  • cerebellum: 1.8 nTPM
  • cerebral cortex: 1.8 nTPM
  • white matter: 1.7 nTPM
  • spinal cord: 1.6 nTPM
  • basal ganglia: 1.5 nTPM

DiseaseUniProt · ClinVar · IEDB · PubMed

Four sources answering four different questions about CTSK.

Disease | AllUniProt

Conditions CTSK is implicated in, by any mechanism.

Disease | GeneticClinVar

134 pathogenic / likely-pathogenic of 458 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)
0.94
gnomAD pLI
0
gnomAD missense Z
1
DepMap mean gene effect
-0.19
DepMap dependency class
selective

Cancer expressionTCGA

Across TCGA tumor cohorts, this protein is over-expressed in roughly 4% 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

Antibody and autoantibody relevanceSeroatlas analysis

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

CTSK is annotated at the cell surface, where native CTSK is exposed to circulating antibodies and is a prime autoantibody target that could block, deplete, or overstimulate it.

Annotation status

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

Canonical record: https://seroatlas.com/gene/CTSK. 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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