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

Area of Science:

• Pharmacology
• Structural Biology
• Biochemistry

Background:

• The micro-opioid receptor (microOR) is a key target for opioid analgesics.
• Current opioid drugs have severe side effects, driving the need for novel modulators.
• Biologics like nanobodies offer advantages over small molecules for GPCR targeting.

Purpose of the Study:

• To describe a novel nanobody, NbE, that selectively binds and antagonizes the micro-opioid receptor.
• To elucidate the molecular mechanism of microOR antagonism by NbE.
• To explore NbE as a basis for developing new microOR-targeting therapeutics.

Main Methods:

• Functional characterization of NbE as an extracellular microOR ligand.
• Determination of the cryo-electron microscopy (cryo-EM) structure of the NbE-microOR complex.
• Design and synthesis of peptide analogs based on NbE's structure.

Main Results:

• NbE selectively binds to and antagonizes the microOR.
• The cryo-EM structure reveals a unique ligand binding mode for NbE, involving interactions with the orthosteric pocket and extracellular loops.
• NbE's β-hairpin loop insertion into the microOR is key to its antagonism.
• Peptide analogs derived from NbE recapitulate its antagonistic activity.

Conclusions:

• Nanobodies can uniquely engage with G protein-coupled receptors (GPCRs) like the microOR.
• NbE provides a structural basis for microOR antagonism and serves as a template for developing novel, lower molecular weight microOR ligands.
• This research opens avenues for developing safer and more selective therapeutics targeting the micro-opioid receptor system.