Transcortin, also known as corticosteroid-binding globulin (CBG) or serpin A6, is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

produced in the liver in animals. In humans it is encoded by the SERPINA6

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. It is an alpha-globulin.

Function

This gene encodes an alpha-globulin protein with

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are inv ...

-binding properties. This is the major transport protein for glucocorticoids and

progestin A progestogen, also referred to as a progestagen, gestagen, or gestogen, is a type of medication which produces effects similar to those of the natural female sex hormone progesterone in the body. A progestin is a ''synthetic'' progestogen. Pro ...

s in the blood of most vertebrates. The gene localizes to a chromosomal region containing several closely related serine protease inhibitors (

serpin Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be id ...

s).

Binding

Transcortin binds several steroid hormones at high rates: *

Cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the '' zona fasciculata'' of the adrenal cortex in the adrenal g ...

- 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. *

Cortisone Cortisone is a pregnene (21-carbon) steroid hormone. It is a naturally-occurring corticosteroid metabolite that is also used as a pharmaceutical prodrug; it is not synthesized in the adrenal glands. Cortisol is converted by the action of the enz ...

* Deoxycorticosterone (DOC) *

Corticosterone Corticosterone, also known as 17-deoxycortisol and 11β,21-dihydroxyprogesterone, is a 21-carbon steroid hormone of the corticosteroid type produced in the cortex of the adrenal glands. It is of minor importance in humans, except in the very rar ...

- About 78% of serum corticosterone is bound to transcortin. *

Aldosterone Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...

- Approximately 17% of serum aldosterone is bound to transcortin, while another 47% is bound to serum albumin. The remaining 36% is free. *

Progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the majo ...

- Approximately 18% of serum progesterone is bound to transcortin, while another 80% of it is bound to serum albumin. The remaining 2% is free. *

17α-Hydroxyprogesterone 17α-Hydroxyprogesterone (17α-OHP), also known as 17-OH progesterone (17-OHP), or hydroxyprogesterone (OHP), is an endogenous progestogen steroid hormone related to progesterone. It is also a chemical intermediate in the biosynthesis of many o ...

In addition, approximately 4% of serum

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristi ...

is bound to transcortin. A similarly small fraction of serum

estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development o ...

is bound to transcortin as well.

Synthesis

Transcortin is produced by the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

and is increased by

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...

Clinical significance

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

References

External links

* * The

MEROPS MEROPS is an online database for peptidases (also known as proteases, proteinases and proteolytic enzymes) and their inhibitors. The classification scheme for peptidases was published by Rawlings & Barrett in 1993, and that for protein inhibitors ...

online database for peptidases and their inhibitors
I04.954
* {{Use dmy dates, date=April 2017 Glycoproteins