Sex hormone-binding globulin and Corticosteroid-binding globulin (SHBG and CBG)

Sex hormone-binding globulin (SHBG) is a plasma glycoprotein that binds sex steroids—primarily testosterone and estradiol—with high affinity, regulating their bioavailability to tissues. SHBG exists as a homodimer, each monomer featuring two laminin G-like domains. It tightly controls the amount of free, active hormone in circulation; levels are influenced by various physiological and pathological conditions, including sex, age, metabolic disease, and pregnancy. Corticosteroid-binding globulin (CBG, also known as transcortin or Serpin A6) is a high-affinity plasma transporter for glucocorticoids (such as cortisol) and progesterone, modulating their delivery to tissues. CBG is a member of the serine protease inhibitor (SERPIN) family but functions primarily as a carrier protein. CBG concentrations decrease in acute stress and inflammatory states, leading to increased free steroid levels. These proteins, though often mentioned together due to functional similarities, are structurally and genetically distinct, and each qualifies as a separate biological entity, not a combined drug target.

Other names

Sex steroid-binding globulinSSBGAndrogen-binding protein (ABP, when produced in testis)TranscortinSerpin A6

Not drug targets; mechanisms involve passive hormone transport and regulation of free, bioactive hormone fractions in plasma