Agonist-specific requirement for a glutamate in transmembrane helix 1 of the oxytocin receptor.
Defining key differences between agonist and antagonist binding to hormone receptors is important and will aid rational drug design. Glu(1.35) in transmembrane helix 1 (TM1) of the human oxytocin receptor (OTR) is absolutely conserved in all OTRs cloned to date. We establish that Glu(1.35) is critical for high affinity binding of agonists (full and partial) but is not required for antagonist binding (peptide or non-peptide). Consequently, the mutant receptor [E1.35A]OTR exhibited markedly decreased OT affinity (>1200-fold) and disrupted second messenger generation. Substitutions of Glu(1.35) by Asp, Gln or Arg were incapable of supporting wild-type OTR agonist binding or signaling. Molecular modeling revealed that Glu(1.35) projects into the receptor's central binding crevice and provides agonist-specific contacts not utilized by antagonists. This study explains why Glu is absolutely conserved at residue-1.35 in all receptors binding OT and related peptides, and provides molecular insight into key differences between agonist-receptor and antagonist-receptor binding modes.
School of Biosciences, University of Birmingham, Edgbaston, Birmingham, UK.
Denise L
DL
Wootten
John
J
Simms
Amelia J
AJ
Massoura
Julie E
JE
Trim
Mark
M
Wheatley
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001120:Arginine / Q000378:metabolism; D001216:Asparagine / Q000378:metabolism; D001665:Binding Sites; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D010121:Oxytocin / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D018045:Receptors, Oxytocin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction
D008565:Membrane Proteins; D018045:Receptors, Oxytocin; D018698:Glutamic Acid; D010121:Oxytocin; D001216:Asparagine; D001120:Arginine