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.

G蛋白偶联受体（G-protein coupled receptor, GPCR）的二聚/寡聚状态一直以来都难以靶向。本研究报道了一类由两个完全相同的催产素模拟物构成的二价配体：该配体在体外可使催产素受体（oxytocin receptor, OTR）的G蛋白信号转导提升三个数量级，在小鼠与斑马鱼的社交行为实验中，其效价强度分别提升100倍与40倍。通过受体诱变实验以及模拟跨膜螺旋（transmembrane helix, TMH）的合成肽干扰实验，我们证实这类超效配体的活性源于其基于跨膜螺旋1-跨膜螺旋2（TMH1-TMH2）界面与二聚体受体的结合。此外，在该结合模式中，仅间隔臂长度约为25埃（∼25 Å）的类似物，才能恰好嵌入二聚体两个原聚体之间的通道样通路。此次新发现的催产素二价配体为靶向二聚体形式的催产素受体以治疗神经发育障碍与精神疾病提供了强有力的工具，同时也为解析G蛋白偶联受体二聚体的特定组装形式提供了通用研究框架。