Transcortin

Transcortin, also known as corticosteroid-binding globulin (CBG) or serpin A6, is a protein produced in the liver in animals. In humans it is encoded by the SERPINA6 gene. It is an alpha-globulin.^[5][6][7]

SERPINA6
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 2VDX, 2VDY, 4BB2, 4C41, 4C49
Identifiers
Aliases	SERPINA6, CBG, serpin family A member 6
External IDs	OMIM: 122500; MGI: 88278; HomoloGene: 20417; GeneCards: SERPINA6; OMA:SERPINA6 - orthologs
Gene location (Human) Chr. Chromosome 14 (human)[1] Band 14q32.13 Start 94,304,248 bp[1] End 94,323,389 bp[1]
Gene location (Mouse) Chr. Chromosome 12 (mouse)[2] Band 12 E|12 52.98 cM Start 103,612,889 bp[2] End 103,623,471 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in liver right lobe of liver gallbladder islet of Langerhans body of pancreas right uterine tube rectum canal of the cervix human kidney mucosa of transverse colon Top expressed in fetal liver hematopoietic progenitor cell human fetus left lobe of liver abdominal wall gallbladder embryo perirhinal cortex entorhinal cortex CA3 field choroid plexus of fourth ventricle More reference expression data BioGPS More reference expression data
Gene ontology Molecular function steroid binding serine-type endopeptidase inhibitor activity lipid binding Cellular component extracellular region extracellular exosome extracellular space Biological process glucocorticoid metabolic process negative regulation of endopeptidase activity transport Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 866 12401 Ensembl ENSG00000277405 ENSG00000170099 ENSMUSG00000060807 UniProt P08185 Q06770 RefSeq (mRNA) NM_001756 NM_007618 RefSeq (protein) NP_001747 NP_031644 Location (UCSC) Chr 14: 94.3 – 94.32 Mb Chr 12: 103.61 – 103.62 Mb PubMed search [3] [4]
Wikidata
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Function

This gene encodes an alpha-globulin protein with corticosteroid-binding properties. This is the major transport protein for glucocorticoids and progestins in the blood of most vertebrates. The gene localizes to a chromosomal region containing several closely related serine protease inhibitors (serpins).^[7]

Binding

Transcortin binds several steroid hormones at high rates:

• Cortisol - Approximately 90% of the cortisol in circulation is bound to transcortin. (The rest is bound to serum albumin.) Cortisol is thought to be biologically active only when it is not bound to transcortin.^{[citation needed]}
• Cortisone^[8]
• Deoxycorticosterone (DOC)^[8]
• Corticosterone - About 78% of serum corticosterone is bound to transcortin.
• Aldosterone - Approximately 17% of serum aldosterone is bound to transcortin, while another 47% is bound to serum albumin. The remaining 36% is free.^[9]
• Progesterone - Approximately 18% of serum progesterone is bound to transcortin, while another 80% of it is bound to serum albumin. The remaining 2% is free.^[10]
• 17α-Hydroxyprogesterone^[8]

In addition, approximately 4% of serum testosterone is bound to transcortin.^[11] A similarly small fraction of serum estradiol is bound to transcortin as well.^{[citation needed]}

Synthesis

Transcortin is produced by the liver and is increased by estrogens.^[12]

Clinical significance

Mutations in this gene are rare. Only four mutations have been described, often in association with fatigue and chronic pain.^[13] The mechanism for these symptoms is not known. This condition must be distinguished from secondary hypocortisolism. Exogenous hydrocortisone does not appear to improve the fatigue.^{[citation needed]}

Hepatic synthesis of corticosteroid-binding globulin more than doubles in pregnancy; that is, bound plasma cortisol in term pregnancy is approximately 2 to 3 times that of nonpregnant women.^[14][15]

See also

• Serpin
• Circaseptan, 7-day biological cycle