Ternary complex between placental lactogen and the extracellular domain ofthe prolactin receptor

The structure of the ternary complex between ovine placental lactogen (oPL) and the extracellular domain (ECD) of the rat prolactin receptor (rPRLR) r eveals that two rPRLR ECDs bind to opposite sides of oPL with pseudo two-fo ld symmetry. The two oPL receptor binding sites differ significantly in the ir topography and electrostatic character. These binding interfaces also in volve different hydrogen bonding and hydrophobic packing patterns compared to the structurally related human growth hormone (hGH)-receptor complexes. Additionally, the receptor-receptor interactions are different from those o f the hGH-receptor complex. The conformational adaptability of prolactin an d growth hormone receptors is evidenced by the changes in local conformatio ns of the receptor binding loops and more global changes induced by shifts in the angular relationships between the N- and C-terminal domains, which a llow the receptor to bind to the two topographically distinct sites of oPL.