Growth hormon complexed with its receptor
Homo sapiens (human)
Control of human growth, muscles, bones and other tissues, is controlled by hormone-like proteins and their inhibitors. The discovery of somato-statin, a 14-residue peptide released from the hypothalamus in the brain, and an inhibitor of the secretion of human growth hormone, contributed to the 1977 award of a Nobel prize in medicine to R.Guillemin. Human growth hormone itself is a protein that effects its influence on growth control through binding to a receptor, the human growth hormone receptor. Human growth hormone receptor is a membrane-bound protein whose extracellular part may exist as a separate protein in serum and capable of binding human growth hormone with the same strength as the membrane-bound receptor. In this function it may help to eliminate human growth hormone from the body when necessary.
Human growth hormone is a four-helix bundle protein with the four helices somewhat tilted relative to each other. The extracellular domain of the growth hormone receptor is a protein with two clearly separated domains that are oriented at a roughly 90 angle to each other resulting in a distinctly L shaped molecule. Two receptor molecules bind to the growth hormone, flanking it from either side. Even though the same residues are involved on either receptor molecule to interact with the hormone, the sites on the hormone that interact are different in type. The complex is thus not symmetric, although its overall shape exhibits some sort of symmetry.
Protein Data Bank (PDB)
author: Arno Paehler