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. Expressed in the anterior lobe of pituitary. N-glycosylated. Overexpression of Gphb5 results in proptosis, elevated serum T4 levels and significantly reduced body weight. Belongs to the glycoprotein hormones subunit beta family.