X-Ray structure of human growth hormone (hGH) in complex with two molecules of its receptor's extracellular domain (hGHbp). The proteins are drawn in ribbon form, with the hGH magenta and the two hGHbp molecules, which together bind one molecule of hGH, each colored in rainbow order from N-terminus (blue) to C-terminus (red). The initial view is along the axis of the hGH's four-helix bundle with the approximate 2-fold axis relating the two hGHbp molecules vertical. [Based on an X-ray structure by Abraham de Vos and Anthony Kossiakoff, Genentech Inc., South San Francisco, California. PDBid 3HHR.]