Model for growth hormone receptor activation based on subunit rotation within a receptor dimer

Abstract

Growth hormone is believed to activate the growth hormone receptor (GHR) by dimerizing two identical receptor subunits, leading to activation of JAK2 kinase associated with the cytoplasmic domain. However, we have reported previously that dimerization alone is insufficient to activate full-length GHR. By comparing the crystal structure of the liganded and unliganded human GHR extracellular domain, we show here that there is no substantial change in its conformation on ligand binding. However, the receptor can be activated by rotation without ligand by inserting a defined number of alanine residues within the transmembrane domain. Fluorescence resonance energy transfer (FRET), bioluminescence resonance energy transfer (BRET) and coimmunoprecipitation studies suggest that receptor subunits undergo specific transmembrane interactions independent of hormone binding. We propose an activation mechanism involving a relative rotation of subunits within a dimeric receptor as a result of asymmetric placement of the receptor-binding sites on the ligand.

S179D prolactin: Antagonistic agony!

“…A potential clue here is offered by work from several other laboratories. First, it seems that growth hormone receptors, erythropoietin receptors and PRLRs are all dimerized prior to ligand binding (Brown et al, 2005;Lu et al, 2006;Qazi et al, 2006). This has long seemed more likely to the author since waiting for random collision of the second receptor with the complex between ligand and first receptor seemed inefficient.…”

“…Instead, as previously illustrated (Walker, 2005) and as shown in figure 2, rotation of the receptor may well be the key. The potential for such a scenario is supported by some elegant work using the erythropoietin receptor (Seubert et al, 2003) and, more recently using the growth hormone receptor (Brown et al, 2005). Each study showed a one amino acid twist in the transmembrane helical region of the receptor to produce altered signaling.…”

Crystal Structure of an Affinity-matured Prolactin Complexed to Its Dimerized Receptor Reveals the Topology of Hormone Binding Site 2

“…This structure identified two asymmetric binding sites on hGH, called sites 1 and 2, which were proposed to trigger hormoneinduced sequential dimerization of the GH receptor, leading to activation (11). More recently, this model has been revisited based on the comparison of unliganded and liganded human GHR-ECD (12); it is now believed that GHR exists as an inactive dimer at the cell membrane, which is activated by hormoneinduced relative rotation of subunits within a dimeric receptor (12). In addition to the characterization of the structural changes occurring in GH and GHR upon their interaction, the GH⅐GHR 2 three-dimensional structures have also largely contributed to the development of GHR antagonists.…”

“…The biochemical, structural, and dynamic properties of GH have been well characterized (11)(12)(13). The determination of the x-ray structure of human GH (hGH) bound to the dimerized extracellular domain (ECD) of its receptor (13) was a crucial step toward the understanding of GHR activation mechanism (14).…”

Biological Determinants of Responsiveness to Growth Hormone: Pharmacogenomics and Personalized Medicine

“…Originally, this mutation was suggested to interfere with receptor homodimerization because it was found to abolish homodimerization of GHBPs. But later, Waters et al [23,24] showed that GHR is constitutively homodimerized at the cell membrane, which presumably involves contacts between transmembrane or juxtamembrane domains of each receptor chain. The activation process mediated by the ligand is assumed to involve a conformational change such as relative rotation of upper and lower domains of the receptor.…”