Purification of Functional CB₁ and Analysis by Site-Directed Fluorescence Labeling Methods

Area of Science:

• Neuroscience
• Biochemistry
• Structural Biology

Background:

• The human cannabinoid receptor type 1 (CB₁) is crucial for neurological processes but difficult to purify functionally.
• This limitation has hindered detailed structural and biophysical studies of CB₁.

Purpose of the Study:

• To develop methods for obtaining pure, detergent-solubilized, functional CB₁.
• To employ site-directed fluorescence labeling (SDFL) to detect conformational changes in CB₁ upon ligand binding.

Main Methods:

• Screening of CB₁-green fluorescent protein chimeras for optimal expression, solubility, and function.
• Purification of tagged CB₁ constructs using immunoaffinity chromatography.
• Site-directed mutagenesis to introduce cysteine residues for labeling with bimane fluorophore.

Main Results:

• Obtained highly pure, detergent-solubilized CB₁ that retains G-protein activation capability (~85% functional).
• SDFL successfully detected conformational changes in CB₁ in response to cannabinoid ligand binding.

Conclusions:

• The developed methods provide pure, functional CB₁ for structural studies (crystallography, cryo-EM).
• SDFL offers insights into the dynamic structural and mechanistic changes of CB₁ during activation and attenuation.