A Genetically Encoded F-19 NMR Probe Reveals the Allosteric Modulation Mechanism of Cannabinoid Receptor 1

Due to the lack of genetically encoded probes for fluorine-19 nuclear magnetic resonance spectroscopy (F-19 NMR), its utility for probing eukaryotic membrane protein dynamics is limited. Here we report an efficient method for the genetic incorporation of an unnatural amino acid (UAA), 3'-trifluoromenthyl-phenylalanine (mtfF), into cannabinoid receptor 1 (CB1) in the Baculovirus Expression System. The probe can be inserted at any environmentally sensitive site, while causing minimal structural perturbation to the target protein. Using F-19 NMR and X-ray crystallography methods, we discovered that the allosteric modulator Org27569 and agonists synergistically stabilize a previously unrecognized pre-active state. An allosteric modulation model is proposed to explain Org27569's distinct behavior. We demonstrate that our site-specific F-19 NMR labeling method is a powerful tool in decoding the mechanism of GPCR allosteric modulation. This new method should be broadly applicable for uncovering conformational states for many important eukaryotic membrane proteins.

Automated summary

A method for genetic incorporation of an unnatural amino acid into a cannabinoid receptor has been developed, revealing a previously unrecognized pre-active state through F-19 NMR and X-ray crystallography methods. An allosteric modulation model is proposed to explain the distinct behavior of the allosteric modulator Org27569. This site-specific F-19 NMR labeling method is a powerful tool for decoding the mechanism of GPCR allosteric modulation.