Ligand binding to receptor proteins functions in signal transduction.


Hormones are molecules that are excreted by exocrine cells and that act at a site distant from their point of excretion by ligating receptor proteins.

Steroid hormones exert their effects by binding to various specific receptor proteins, forming complexes with transcription factors that bind to response elements of genes. Response elements are sequences of DNA that are located in promoter or enhancer sequences, and which contain short consensus sequences.

Estrogen response element (ERE) – estrogen binds to the estrogen receptor transcription factor; consensus sequence AGGTCANNNTGACCT.

Glucocorticoid response element (GRE) – glucocorticoids bind to the glucocorticoid receptor transcription factor; consensus sequence AGAACANNNTGTTCT

Hormones such as adrenaline, glucagon, luteinizing hormone (LH), parathyroid hormone (PTH), and adrenocorticotropic hormone (ACTH) interact with GPCRs to cause an increase in the cyclic nucleotide, second messenger, cAMP. Atrial natriuretic peptide (ANP) interacts with GPCRs to elevate levels of the cyclic nucleotide, second messenger, cGMP. The the peptide/protein hormones vasopressin, thyroid-stimulating hormone (TSH), and angiotensin, via activate phospholipase C (PLC).

Ca2+ ions, which are the most widely employed second messengers, are involved in the secretion of hormones such as insulin.

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