Design and Characterization of Superpotent Bivalent Ligands Targeting Oxytocin Receptor Dimers via a Channel-Like Structure

Dimeric/oligomeric
states of G-protein coupled receptors have been
difficult to target. We report here bivalent ligands consisting of
two identical oxytocin-mimetics that induce a three order magnitude
boost in G-protein signaling of oxytocin receptors (OTRs) in vitro and a 100- and 40-fold gain in potency in vivo in the social behavior of mice and zebrafish. Through
receptor mutagenesis and interference experiments with synthetic peptides
mimicking transmembrane helices (TMH), we show that such superpotent
behavior follows from the binding of the bivalent ligands to dimeric
receptors based on a TMH1-TMH2 interface. Moreover, in this arrangement,
only the analogues with a well-defined spacer length (∼25 Å)
precisely fit inside a channel-like passage between the two protomers
of the dimer. The newly discovered oxytocin bivalent ligands represent
a powerful tool for targeting dimeric OTR in neurodevelopmental and
psychiatric disorders and, in general, provide a framework to untangle
specific arrangements of G-protein coupled receptor dimers.