Characterizing and exploiting "allosteric crosstalk" amongst pain receptors

The National Institute on Drug Abuse awarded The Johns Hopkins University $466,363 on June 1, 2026, under the Drug Use and Addiction Research Programs (CFDA 93.279) to characterize allosteric crosstalk among opioid and endogenous neuromodulator receptors.

The project uses cryo-electron microscopy to determine high-resolution structures of the mu-opioid receptor in active and inactive states bound to cannabinoids and neuropeptides including oxytocin. The work advances time-resolved cryo-EM methodologies to visualize intermediate conformational states and construct molecular movies of the full activation and inactivation pathway of the receptor. By elucidating how endogenous neuromodulators such as endocannabinoids and oxytocin allosterically modulate mu-opioid receptor signaling at atomic resolution, the research aims to identify previously unrecognized allosteric sites and control points that could yield novel interventions for opioid use disorder.

Performance is at Baltimore, Maryland. The project period runs from June 1, 2026, through April 30, 2031.

Abstract

Opioid receptors not only mediate pain relief but also act as the targets of potent exogenous opioids that are devastatingly addictive and cause overdose deaths. The principal target for both analgesia and addiction of exogenous opioids is the μ-opioid receptor (ΜOR). While traditionally thought to be regulated exclusively by opioids, recent work from our group has detailed an unexpected layer of complexity: endogenous neuromodulators such as endocannabinoids and oxytocin - classically associated with their own independently signaling receptors that regulate mood, pain, inflammation, and social behavior - can directly work to allosterically modulate ΜOR signaling. This unanticipated ligand-mediated crosstalk opens an entirely new dimension in opioid receptor pharmacology and suggests that targeting these pathways could yield novel interventions for opioid use disorder (OUD) and related conditions. The central goal of this project is to elucidate, at atomic resolution, the molecular mechanisms by which endogenous neuromodulators influence ΜOR structure and function. We will employ state-of-the-art cryo-electron microscopy (cryoem) approaches to determine high- resolution structures of ΜOR in both its active and inactive states, bound to cannabinoids and neuropeptides like oxytocin. Critically, we will advance methodological innovations in time-resolved cryoem to directly visualize the intermediate conformational states and the full activation/inactivation pathway of the receptor as IT transitions between these endpoints. This will allow US, for the first time, to construct "molecular movies" that reveal the stepwise mechanisms by which natural modulators influence receptor activation, allostery, and signaling bias. Through these detailed structural insights, we aim to identify previously unrecognized allosteric sites and intermediate states that serve as control points for selective pharmacological intervention. These discoveries will inform the rational design of new therapeutic strategies that harness or mimic the brain's own modulatory systems, offering a pathway to safer, more targeted treatments for OUD, pain, and overdose. In summary, this project will not only clarify the molecular basis of opioid receptor regulation in the brain, but will also set the stage for mechanism-driven drug discovery to address the current opioid crisis and advance our broader understanding of gpcr biology.