Cannabidiol (CBD) modulates the effects of THC in the brain by binding to a specific site on the CB1R receptor, reducing its activation. This interaction may explain why CBD attenuates some effects of THC, such as anxiety and paranoia. The study identifies a new intracellular binding site for CBD, which may help in the development of new drugs that better control the effects of cannabinoids in the body.
The cannabinoid receptor 1 (CB1R) is a protein found in the nervous system and plays a fundamental role in several functions of the body, such as pain control, appetite regulation, metabolism and stress responses. For this reason, it has been widely studied as a possible therapeutic target to treat conditions such as obesity, chronic pain, vomiting and metabolic syndrome.
Many substances can interact with this receptor, activating or modulating its function. Tetrahydrocannabinol (THC), for example, is a compound present in marijuana that directly activates the CB1R.
Cannabidiol (CBD), another compound from the plant, does not activate the receptor in the same way, but functions as a negative allosteric modulator (NAM), altering its activity indirectly. However, the exact way in which cannabidiol interacts with CB1R was not yet fully understood.
Previous research has used different techniques to try to identify the exact locations where modulator substances, such as cannabidiol, bind to CB1R.
Structural studies using X-ray crystallography had identified a specific site for another negative allosteric modulator called ORG27569, which binds to an external region of the receptor, within the cell membrane.
On the other hand, computer simulations suggested that cannabidiol could bind to multiple sites within the CB1R structure, but there was no consensus on which one would be the main one. Some studies even suggested that cannabidiol could occupy the same site as ORG27569, but this still needed to be investigated in more depth.
To clarify this question, researchers from the University of Mississippi, USA, carried out a detailed study combining several advanced techniques.
First, they used computational modeling to predict the possible binding sites of cannabidiol to CB1R, including molecular docking (a method that simulates how a molecule fits into a protein) and molecular dynamics (MD) simulations, which analyze the behavior of molecules over time.
They also performed free energy binding calculations, which help determine which site is most favorable for cannabidiol to interact with the receptor. Finally, they performed laboratory mutagenesis experiments, in which they altered specific parts of the CB1R to test the importance of certain amino acid residues in binding cannabidiol.
The results of these analyses showed that cannabidiol can bind to two distinct sites on the CB1R. The first is the same site previously identified for ORG27569, on the outside of the receptor within the cell membrane.
The second binding site for cannabidiol is inside the cell, in a specific region of the CB1 receptor, between three of its helices and a structure called helix 8. This site had never been identified before in this receptor, but it is similar to areas already known in other proteins of the same family, which play important roles in the regulation of various functions in the body.
To confirm which of these two sites was most important for cannabidiol action, the scientists modified specific residues within each region and assessed how this affected the binding of the substance to CB1R.
They found that mutations in residues S4018.47 and D4038.49 increased the binding of another substance used in the study, indicating that these parts of the receptor are crucial for interaction with cannabidiol.
Thus, the results showed that cannabidiol preferentially binds to an internal region of the CB1 receptor, close to three main structural segments and an additional helix.
Within this area, cannabidiol interacts with specific parts of the protein that appear to be essential for this binding, which may influence how the receptor functions and modulate its effects in the body.
This discovery is extremely relevant because it helps to better understand how cannabidiol acts in the body and may contribute to the development of new medicines.
The fact that cannabidiol binds to an intracellular allosteric site may explain its ability to modulate different receptors in the body, which may be related to its diverse therapeutic effects.
In addition, this information can be used to design new allosteric modulators of the CB1R that are more selective and effective, paving the way for more precise treatments with fewer side effects.
READ MORE:
Determination of the Negative Allosteric Binding Site of Cannabidiol at the CB1 Receptor: A Combined Computational and Site-Directed Mutagenesis Study
Pankaj Pandey, Ayat Zagzoog, Robert B. Laprairie, William M. Neal, Robert J. Doerksen, Amar G. Chittiboyina
ACS Chemical Neuroscience, Vol 16/Issue 3, January 15, 2025
Abstract:
Cannabinoid receptor 1 (CB1R) has been extensively studied as a potential therapeutic target for various conditions, including pain management, obesity, emesis, and metabolic syndrome. Unlike orthosteric agonists such as Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD) has been identified as a negative allosteric modulator (NAM) of CB1R, among its other pharmacological targets. Previous computational and structural studies have proposed various binding sites for CB1R NAMs. An X-ray crystal structure revealed a binding site for the NAM, ORG27569, at an extrahelical location within the inner leaflet of the membrane. In contrast, multiple computational studies have previously proposed several potential allosteric binding sites for CBD within the CB1R structure. Given that a prior structural study suggested CBD might occupy the same site as ORG27569, we conducted a comprehensive investigation of potential CBD binding sites using molecular docking, molecular dynamics (MD) simulations, metadynamics (MTD) simulations, binding free-energy calculations, and in vitro mutagenesis experiments. Molecular docking, MD, and MTD simulations results, along with binding free-energy calculations, suggest that CBD may potentially bind to either the same extrahelical site as ORG27569 or a previously unidentified intracellular site located near TMHs 2, 6, and 7 and helix 8. This intracellular site is consistent with allosteric binding sites observed in other G protein-coupled receptors (GPCRs). To establish the most favorable allosteric site for CBD, we conducted site-directed mutagenesis of key residues at each site. Mutations at S4018.47ΔA and D4038.49ΔA augmented the binding of [3H]-SR141716A, suggesting these residues play critical roles in CBD binding. As a result, the combined computational and mutagenesis results identified a binding site for CBD between TMHs 2, 6, and 7 and helix 8, involving residues Y1532.40, I1562.43, M3376.29, L3416.33, S4018.47, and D4038.49. These findings provide valuable insights into how CBD binds to CB1R, thereby informing the rational design of new, selective, and potent NAMs. Moreover, the elucidation of this previously unexplored allosteric site might explain the polypharmacology of CBD due to structural conservation among Class A GPCRs.
Commenti