Seroatlas · Human Serome Atlas

C3orf18

Uncharacterized protein C3orf18

Also known as: CC018_HUMAN, G20

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

Protein identityUniProt · HPA

UniProt accession
Q9UK00
Gene
C3orf18
Ensembl
ENSG00000088543
Chromosome
3
Canonical length
162 aa
Protein class
Predicted intracellular proteins, Predicted membrane proteins
Subcellular location
Cytosol

OverviewNCBI Gene

Predicted to be located in membrane. [provided by Alliance of Genome Resources, Jul 2025]

Canonical amino-acid sequenceUniProt

162 residues, UniProt reviewed canonical sequence.

>Q9UK00|C3orf18
     1  MNSRTASARG WFSSRPPTSE SDLEPATDGP ASETTTLSPE ATTFNDTRIP DAAGGTAGVG
    61  TMLLSFGIIT VIGLAVALVL YIRKKKRLEK LRHQLMPMYN FDPTEEQDEL EQELLEHGRD
   121  AASVQAATSV QAMQGKTTLP SQGPLQRPSR LVFTDVANAI HA

LocalizationUniProt · AlphaFold · HPA

Whether an antibody against C3orf18 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
Unknown
Secreted
No
Transmembrane segments
1
Mean surface accessibility (rSASA)
0.63
Highest tissue expression
55 nTPM

Expression across tissuesHPA

Tissue

  • cerebellum: 55 nTPM
  • skeletal muscle: 34 nTPM
  • heart muscle: 32 nTPM
  • choroid plexus: 27 nTPM
  • retina: 26 nTPM
  • parathyroid gland: 26 nTPM

Single-cell type

  • late spermatids: 105 nCPM
  • early spermatids: 65 nCPM
  • cardiomyocytes: 53 nCPM
  • late primary spermatocytes: 18 nCPM
  • parietal cells: 14 nCPM
  • retinal pigment epithelial cells: 13 nCPM

Immune cell

  • MAIT T-cell: 6.3 nTPM
  • naive CD8 T-cell: 6.2 nTPM
  • gdT-cell: 5.1 nTPM
  • naive CD4 T-cell: 5 nTPM
  • memory CD8 T-cell: 4.8 nTPM
  • memory CD4 T-cell: 4.3 nTPM

Brain region

  • cerebellum: 31 nTPM
  • choroid plexus: 22 nTPM
  • hypothalamus: 22 nTPM
  • thalamus: 22 nTPM
  • midbrain: 21 nTPM
  • medulla oblongata: 18 nTPM

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)
1.69
gnomAD pLI
0
gnomAD missense Z
0.53
DepMap mean gene effect
-0.06
DepMap dependency class
none

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

Cellular components

Protein domainsUniProt · Pfam · InterPro

  • Uncharacterized protein C3orf18-like

KeywordsUniProt

Antibody and autoantibody relevanceSeroatlas analysis

Seroatlas reads C3orf18 as an antibody target. Whether an autoantibody or antibody against C3orf18 could matter depends on whether native C3orf18 is physically reachable, whether the body needs it intact, and whether it acts in a disease-relevant tissue.

C3orf18 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 C3orf18 as an autoantigen. Seroatlas presents hypothesis context only and does not manufacture a known-serology claim.

Canonical record: https://seroatlas.com/gene/C3orf18. 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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