New structural insights into the apelin receptor: identification of key residues for apelin binding

FASEB J. 2015 Jan;29(1):314-22. doi: 10.1096/fj.14-256339. Epub 2014 Oct 30.


Apelin is the endogenous ligand of the orphan 7-transmembrane domain GPCR APJ, now named the apelin receptor (ApelinR). Apelin plays a prominent role in body fluid and cardiovascular homeostasis. To better understand the structural organization of the ApelinR, we built 3 homology 3-dimensional (3D) models of the human ApelinR using the validated cholecystokinin receptor-1 3D model or the X-ray structures of the β2-adrenergic and CXCR4 receptors as templates. Docking of the pyroglutamyl form of apelin 13 (pE13F) into these models revealed the conservation at the bottom of the binding site of a hydrophobic cavity in which the C-terminal Phe of pE13F was embedded. In contrast, at the top of the binding site, depending on the model, different interactions were visualized between acidic residues of the ApelinR and the basic residues of pE13F. Using site-directed mutagenesis, we showed that Asp 92, Glu 172, and Asp 282 of rat ApelinR are key residues in apelin binding by interacting with Lys 8, Arg 2, and Arg 4 of pE13F, respectively. These residues are only seen in the CXCR4-based ApelinR 3D model, further validating this model. These findings bring new insights into the structural organization of the ApelinR and the mode of apelin binding.

Keywords: APJ; G protein–coupled receptor; homology models; molecular modeling; site-directed mutagenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Animals
  • Apelin
  • Apelin Receptors
  • Binding Sites / genetics
  • Conserved Sequence
  • Cyclic AMP / biosynthesis
  • Humans
  • Intercellular Signaling Peptides and Proteins / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Multiprotein Complexes / chemistry
  • Mutagenesis, Site-Directed
  • Protein Conformation
  • Rats
  • Receptors, G-Protein-Coupled / chemistry*
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / metabolism*
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Structural Homology, Protein


  • APLN protein, human
  • APLNR protein, human
  • Apelin
  • Apelin Receptors
  • Aplnr protein, rat
  • Intercellular Signaling Peptides and Proteins
  • Multiprotein Complexes
  • Receptors, G-Protein-Coupled
  • Recombinant Fusion Proteins
  • Cyclic AMP