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Structural basis of μ-opioid receptor targeting by a nanobody antagonist

Affiliations
  • 1Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland.
  • 2Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland.
  • 3Departments of Chemistry and Bioengineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium.
  • 4Department of Plant Sciences, University of Geneva, Geneva, Switzerland.
  • 5Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, USA.
  • 6Confo Therapeutics N.V., Gent, Belgium.
  • 7Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium.
  • 8VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium.
  • 9Department of Pharmaceutical Chemistry, University of California, San Francisco, CA, USA.
  • 10Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland. andreas.boland@unige.ch.
  • 11Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland. miriam.stoeber@unige.ch.

Published on:

October 9, 2024

Abstract

The μ-opioid receptor (μOR), a prototypical G protein-coupled receptor (GPCR), is the target of opioid analgesics such as morphine and fentanyl. Due to the severe side effects of current opioid drugs, there is considerable interest in developing novel modulators of μOR function. Most GPCR ligands today are small molecules, however biologics, including antibodies and nanobodies, represent alternative therapeutics with clear advantages such as affinity and target selectivity. Here, we describe the nanobody NbE, which selectively binds to the μOR and acts as an antagonist. We functionally characterize NbE as an extracellular and genetically encoded μOR ligand and uncover the molecular basis for μOR antagonism by determining the cryo-EM structure of the NbE-μOR complex. NbE displays a unique ligand binding mode and achieves μOR selectivity by interactions with the orthosteric pocket and extracellular receptor loops. Based on a β-hairpin loop formed by NbE that deeply protrudes into the μOR, we design linear and cyclic peptide analogs that recapitulate NbE’s antagonism. The work illustrates the potential of nanobodies to uniquely engage with GPCRs and describes lower molecular weight μOR ligands that can serve as a basis for therapeutic developments.

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