Identifying Bioactive Conformation of GnRH1 Based on Molecular Docking of NMR Conformers to GnRH1R and mAbs

GnRH1 binds to its receptor GnRH1R to stimulate release of FSH and LH. Earlier NMR analysis had reported several possible conformers of GnRH1; however, the biologically active conformation of GnRH1 is not identified so far. Here, molecular docking of different NMR conformers of GnRH1 to GnRH1R is performed. Based on: (a) residues of GnRH1R interacting with antagonist elagolix (as ligand-binding pocket), (b) intermolecular hydrogen bonds (for specificity of interaction), and (c) total intermolecular non-covalent interactions (for stability of interaction), one NMR conformation, having an asymmetric U-turn reverse coil structure with a beta strand comprised of residues Gly6 and Leu7, is identified as the bioactive conformation of GnRH1. Further, the identified bioactive NMR conformation of GnRH1 is used to explain in vivo GnRH1-neutralizing ability of monoclonal antibody (mAb) F1D3C5 and lack of neutralization by another mAb E2D2H12. In mice, F1D3C5 completely blocks estrus cycle, while E2D2H12, despite having a relatively higher affinity for GnRH1 in ELISA, does not alter the estrus cycle. Molecular docking of the identified bioactive NMR conformation of GnRH1 to homology models of scFv attributes in vivo neutralizing ability of F1D3C5 to structure-specific recognition of GnRH1. The bioactive conformation of GnRH1 identified here could guide co-crystallization studies, design of analogs and GnRH1 vaccination efforts.