Identification of a Novel Ligand Binding Residue Arg^38(1.35)in the Human Gonadotropin-Releasing Hormone Receptor

Abstract

Delineation of peptide ligand binding sites is of fundamental importance in rational drug design and in understanding ligandinduced receptor activation. Molecular modeling and ligand docking to previously experimentally identified binding sites revealed a putative novel interaction between the C terminus of gonadotropin-releasing hormone (GnRH)

Role of the Transmembrane Domain 4/Extracellular Loop 2 Junction of the Human Gonadotropin-releasing Hormone Receptor in Ligand Binding and Receptor Conformational Selection

“…The crystal structures of bovine rhodopsin, the ␤-ARs, and A 2A adenosine receptor reveal the conformational diversity of ECLs, especially ECL2 (35), but all of the above GPCR structures predict ECL2 as part of the ligand binding pocket (36,37). A ␤IIЈ-turn conformation of GnRH I (derived from a recent NMR structure) was docked into the active state model according to previous experimentally determined interactions (2,10,12). In our current GnRH receptor models, the 7-TM domains were constructed based on ␤ 2 -AR and opsin, whereas the ECLs and intracellular loops were modeled ab initio by means of a molecular mechanics-based algorithm implemented in LOOPER (28), which often finds near native loop conformations.…”

“…It is likely to involve interactions with the extracellular loops as well as the TM domains. Interestingly, the molecular model of GnRH I docking to the human GnRH receptor suggests a potential interaction between Trp 3 of the ligand with a region at the extracellular end of TM4 leading into ECL2 (12).…”

“…The models with the best scores were selected for GnRH docking and molecular dynamics (MD) simulations. A ␤IIЈ-type turn conformation of GnRH I (derived from an NMR structure (PDB code 1YY1)) was docked into the active state model according to the previously experimentally identified contact points between GnRH and its receptor (pGlu 1 (2,3,10,12)). The above prepared molecules were inserted into the membrane bilayer.…”

Salt Bridges Overlapping the Gonadotropin-Releasing Hormone Receptor Agonist Binding Site Reveal a Coincidence Detector for G Protein-Coupled Receptor Activation

“…This conformation of GnRH was manually docked in the active conformation of the receptor to comply with experimentally identified contacts between GnRH analogs and receptor residues: pGlu 1 (Sealfon et al, 1997;Flanagan et al, 2000;Hoffmann et al, 2000;Hövelmann et al, 2002;Coetsee et al, 2008;Millar et al, 2008;Stewart et al, 2008). A similar mode of GnRH docking has been proposed and experimentally validated .…”

Histidine7.36(305) in the conserved peptide receptor activation domain of the gonadotropin releasing hormone receptor couples peptide binding and receptor activation

“…However, only a few of the proposed contacts have been validated with appropriate ligand modifications Sealfon et al, 1997). The Arg 1.35(38) and Asn 2.65(102) residues (Ballesteros and Weinstein receptor residue numbering system, see under "Materials and Methods" for explanation) at the extracellular ends of the first and second transmembrane helices (TM) of the GnRH receptor contribute to recognition of the carboxy-terminal Gly 10 NH 2 moiety of GnRH (Davidson et al, 1996;Stewart et al, 2008), an acidic residue at the extracellular end of TM7 recognizes the basic Arg 8 residue, which is important for high affinity binding of GnRH (Flanagan et al, 1994;Fromme et al, 2001) and the Tyr 6.58(290) side chain determines recognition of Tyr 5 of GnRH (Coetsee et al, 2008). Receptor interactions of the amino-terminal residues of GnRH that are important for agonist activity are less well-defined.…”