Scientists Identified a Key Amino Acid in the CB1 Receptor That Determines Which Cannabinoids Can Bind | Research

The takeaway

Mutating a single amino acid (Ser7.39) in the CB1 receptor eliminated binding for some cannabinoids while leaving others unaffected, revealing that different cannabinoids dock at different parts of the receptor.

Read this if you're interested in the molecular details of how cannabinoids interact with brain receptors.

One amino acid mutation abolished CP55,940 binding but left WIN55,212-2 unaffected

What the researchers found

Researchers mutated two serine residues in the human CB1 cannabinoid receptor to determine their roles in ligand binding.

The Ser7.39 mutation (S7.39A) completely abolished high-affinity binding of CP55,940, a widely used synthetic cannabinoid, and dramatically reduced binding of HU210 and AM4056 (50- to 100-fold). Their activation potency dropped by over 200-fold.

Remarkably, the same mutation had virtually no effect on WIN55,212-2 binding, demonstrating that this structurally different cannabinoid binds to a distinct site on the receptor. The Ser2.60 mutation had no effect on any tested ligand.

Molecular modeling suggested that Ser7.39 induces a bend in the receptor's transmembrane helix 7, creating a docking space specifically required by CP55,940-type compounds.

Why it matters

Understanding exactly how different cannabinoids interact with the CB1 receptor at the molecular level is essential for designing targeted drugs that activate specific aspects of cannabinoid signaling while avoiding unwanted effects.

The numbers in context

S7.39A mutation: complete loss of CP55,940 binding; 50-100 fold reduction in HU210 and AM4056 affinity; >200-fold reduction in HU210/AM4056 potency. WIN55,212-2 binding: unaffected. S2.60A mutation: no effect on any ligand.

How the study worked

Researchers created mutant human CB1 receptors (S7.39A and S2.60A) stably expressed in human kidney cells. They tested radioligand binding and GTPgammaS functional assays with four different cannabinoid ligands (CP55,940, WIN55,212-2, HU210, AM4056). Molecular modeling was used to explain the structural basis of the findings.

What this study cannot tell us

The study used an artificial expression system (human kidney cells), which may not fully represent how CB1 receptors behave in neurons. Only four ligands were tested. Molecular modeling predictions need experimental validation.

How to read the evidence

This is a molecular pharmacology study using mutant receptors in cell culture. It provides mechanistic insights but is far from clinical application.

When this study was published

Published in 2007. Crystal structures of the CB1 receptor have since been solved (2016-2017), confirming and extending many of these computational predictions.

The bigger picture

This study demonstrated that the CB1 receptor has multiple binding modes for different cannabinoid structures. This molecular insight has implications for drug design, potentially allowing researchers to create cannabinoids that target specific binding conformations for more precise therapeutic effects.

Questions still open

How does THC itself interact with Ser7.39? Could drugs be designed to exploit the different binding sites on CB1 for more selective therapeutic effects?

Common questions

Why does this matter for medicine?

If different cannabinoids bind to different parts of the CB1 receptor, scientists could potentially design drugs that only activate the beneficial aspects of cannabinoid signaling while avoiding unwanted effects like intoxication.

What is CP55,940?

CP55,940 is a synthetic cannabinoid widely used in laboratory research. It is much more potent than THC and binds to CB1 receptors with very high affinity. It is not used medicinally.

Read the original research

Mutation studies of Ser7.39 and Ser2.60 in the human CB1 cannabinoid receptor: evidence for a serine-induced bend in CB1 transmembrane helix 7.

Molecular pharmacology, 71(6), 1512-24

View on PubMed ↗

Citation

Kapur, Ankur; Hurst, Dow P; Fleischer, Daniel; Whitnell, Rob; Thakur, Ganesh A; Makriyannis, Alexandros; Reggio, Patricia H; Abood, Mary E. (2007). Mutation studies of Ser7.39 and Ser2.60 in the human CB1 cannabinoid receptor: evidence for a serine-induced bend in CB1 transmembrane helix 7.. Molecular pharmacology, 71(6), 1512-24.