Functions as a heterodimeric glycoprotein hormone with GPHA2 able to bind and activate the thyroid-stimulating hormone receptor (TSHR), leading to increased cAMP production. Plays a central role in controlling thyroid cell metabolism. Heterodimer with GPHA2; this heterodimer interacts with thyroid-stimulating hormone receptor (TSHR), and hence stimulates cAMP production. Highly expressed in brain and at low levels in pituitary. Also found in retina, testis and skin but not in pancreas, parotid, kidney, stomach, liver, colon, small intestine, thyroid, brain or adrenal gland. In pituitary, colocalizes with ACTH, suggesting that it is located in corticotrophs. N-glycosylated. Belongs to the glycoprotein hormones subunit beta family.