An original approach to measure ligand/receptor binding affinity in non-purified samples

Area of Science:

• Biochemistry
• Biophysics
• Pharmacology

Background:

• Traditional methods for determining ligand binding affinities often require protein purification, labeling, or immobilization.
• These processes can disrupt the native conformation and functionality of membrane proteins, complicating accurate measurements.
• Studying membrane proteins in their native environment is crucial for understanding their biological roles.

Purpose of the Study:

• To develop a novel experimental procedure using microscale thermophoresis (MST) for determining ligand binding affinities to membrane proteins directly from cell membrane fragments.
• To overcome challenges in measuring membrane protein concentrations and accounting for non-specific binding in crude samples.
• To validate the method by accurately determining the binding affinity of ligands to the dopamine D2 receptor (D2R).

Main Methods:

• Utilized microscale thermophoresis (MST) on intact cell membrane fragments, avoiding protein purification and extraction.
• Developed strategies to determine the concentration of the target membrane protein (D2R) within crude membrane samples.
• Implemented methods to minimize or correct for non-specific ligand binding to cell fragments during MST analysis.

Main Results:

• Successfully quantified dopamine D2 receptor (D2R) concentration in cell membrane fragments at approximately 36.8 ± 2.6 pmol/mg.
• Determined the dissociation constant (K_D) for D2R ligands with high accuracy (approximately 5.3 ± 1.7 nM), closely matching reported values.
• Demonstrated the feasibility of applying MST directly to membrane fragments for reliable ligand binding affinity studies.

Conclusions:

• The developed MST method provides a robust and direct approach for measuring ligand binding affinities to membrane proteins in their native-like environment.
• This novel technique overcomes significant limitations associated with traditional methods, particularly for challenging membrane protein targets.
• The detailed experimental protocol allows for broad applicability to various membrane proteins, advancing drug discovery and biological research.