Related Experiment Video
Updated: Dec 27, 2025

Preparation and Delivery of Protein Microcrystals in Lipidic Cubic Phase for Serial Femtosecond Crystallography
Published on: September 20, 2016
Desmetramadol Is Identified as a G-Protein Biased µ Opioid Receptor Agonist
John A Zebala1, Aaron D Schuler1, Stuart J Kahn1
1Department of Chemistry and Preclinical Development, Syntrix Pharmaceuticals, Auburn, WA, United States.
Abstract:
Tramadol is widely used globally and is the second most prescribed opioid in the United States. It treats moderate to severe pain but lethal opioid-induced respiratory depression is uncommon even in large overdose. It is unknown why tramadol spares respiration. Here we show its active metabolite, desmetramadol, is as effective as morphine, oxycodone and fentanyl in eliciting G protein coupling at the human µ opioid receptor (MOR), but surprisingly, supratherapeutic concentrations spare human MOR-mediated βarrestin2 recruitment thought to mediate lethal opioid-induced respiratory depression.
Related Concept Videos
Opioid Receptors: Overview
Opioid Analgesics: Synthetic and Semisynthetic Opioids
Analgesia and Pain Management
Opioid Analgesics: Morphine and Other Natural Cogeners
Drug-Receptor Interaction: Agonist
Agonists can bind to receptors in different ways. Some agonists bind directly to the receptor's active site, mimicking the endogenous...
GPCR Desensitization

