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Sex hormone binding globulin



Crystal structure of SHBG binding dihydrotestosterone. From PDB 1D2S.[1]
Sex hormone-binding globulin, Androgen-binding protein
Identifiers
Symbol SHBG
Alt. Symbols ABP
Entrez 6462
HUGO 10839
OMIM 182205
RefSeq NM_001040
UniProt P04278
Other data
Locus Chr. 17 p13-p12

Sex hormone-binding globulin (SHBG) is a glycoprotein that binds to sex hormones, specifically testosterone and estradiol. Other steroid hormones such as progesterone, cortisol, and other corticosteroids are bound by transcortin.

Additional recommended knowledge

Contents

Transport of sex hormones

These sex hormones circulate in the bloodstream, bound mostly to SHBG and to some degree bound to serum albumin. Only a small fraction is unbound, or "free," and thus biologically active and able to enter a cell and activate its receptor. The SHBG inhibits the function of these hormones. Thus bioavailability of sex hormones is influenced by the level of SHBG.

SHBG production

SHBG is produced by the liver cells and is released into the bloodstream. Other sites that produce SHBG are the brain, uterus, and placenta and vagina. In addition SHBG is produced by the testes; testes-produced SHBG is also called androgen-binding protein. The gene for SHBG is located on chromosome 17.

Control

SHBG levels appear to be controlled by a delicate balance of enhancing and inhibiting factors. Its level is decreased by high levels of insulin and insulin-like growth factor 1 (IGF-1). Also, high androgen levels decrease SHBG, while high estrogen and thyroxine levels increase it.

However, recent evidence suggests that it is the livers production of fats that reduces SHBG levels[2], not any direct effect of insulin and specific genetic mechanisms have been found that do this.

Conditions with high or low levels

Conditions with low SHBG include polycystic ovary syndrome, diabetes, and hypothyroidism. Conditions with high SHBG include pregnancy, hyperthyroidism, and anorexia nervosa. There has recently been research to link high SHBG levels with breast and testicular cancer as well.

Measurement of sex hormones

When determining levels of circulating estradiol or testosterone, either a total measurement could be done that includes the "free" and the bound fractions, or only the "free" hormone could be measured. A free androgen index expresses the ratio of testosterone to the sex hormone binding globulin and can be used to summarise the activity of free testosterone.

See also

References

  1. ^ Grishkovskaya I, Avvakumov GV, Sklenar G, Dales D, Hammond GL, Muller YA (2000). "Crystal structure of human sex hormone-binding globulin: steroid transport by a laminin G-like domain". EMBO J 19 (4): 504–12. doi:10.1093/emboj/19.4.504. PMID 10675319.
  2. ^ http://www.physorg.com/news113902673.html


 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sex_hormone_binding_globulin". A list of authors is available in Wikipedia.
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