Molecular mechanism of allosteric modulation for the cannabinoid receptor CB1

Given the promising clinical value of allosteric modulators of G protein-coupled-receptors (GPCRs), mechanistic understanding of how these modulators alter GPCR function is of significance. Here, we report the crystallographic and cryo-electron microscopy structures of the cannabinoid receptor CB1 bound to the positive allosteric modulator (PAM) ZCZ011. These structures show that ZCZ011 binds to an extrahelical site in the transmembrane 2 (TM2)-TM3-TM4 surface. Through (un)biased molecular dynamics simulations and mutagenesis experiments, we show that TM2 rearrangement is critical for the propagation of allosteric signals. ZCZ011 exerts a PAM effect by promoting TM2 rearrangement in favor of receptor activation and increasing the population of receptors that adopt an active conformation. In contrast, ORG27569, a negative allosteric modulator (NAM) of CB1, also binds to the TM2-TM3-TM4 surface and exerts a NAM effect by impeding the TM2 rearrangement. Our findings fill a gap in the understanding of CB1 allosteric regulation and could guide the rational design of CB1 allosteric modulators.

Automated summary

This study presents the crystallographic and cryo-electron microscopy structures of CB1 receptor bound to the allosteric modulator ZCZ011. The results show that ZCZ011 induces rearrangement of TM2, promoting receptor activation and increasing the population of active receptors. In contrast, the negative allosteric modulator ORG27569 inhibits TM2 rearrangement. These findings provide insights into CB1 allosteric regulation and have implications for the rational design of allosteric modulators.