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Sex hormone binding globulin
From Wikipedia, the free encyclopedia
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| Crystal structure of SHBG binding dihydrotestosterone. From PDB 1D2S.[1] | |
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Sex hormone-binding globulin, Androgen-binding protein
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| 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.
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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 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.
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 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.
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.
- ^ 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.
- ^ http://www.physorg.com/news113902673.html
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| Hormone | Follistatin - Growth hormone binding protein - Insulin-like growth factor binding protein - Neurophysins (Neurophysin I, II) Sex hormone binding globulin/Androgen binding protein - Transcortin - Thyroxine-binding globulin - Transthyretin |
| Metal/element | calcium (Calcium-binding protein, Calmodulin-binding proteins) - copper (Ceruloplasmin) - iron (Iron-binding proteins, Transferrin receptor) |
| Vitamin | Retinol binding protein (4) - Transcobalamins |
| Other | Acyl carrier protein - Adaptor protein - Cholesterylester transfer protein - F-box protein - GTP-binding protein - Latent TGF-beta binding protein - Light-harvesting complex - Membrane transport protein |
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| Angiostatin - Haemopexin - Beta-2 microglobulin - Factor H - Plasminogen - Properdin - Sex hormone binding globulin - Transferrin |