Fluor NMR study of amino acid derived ligand to study TSPO

Translocator protein (TSPO, 18 kDa), previously known as peripheral-type benzodiazepine receptor, is an evolutionarily conserved membrane protein involved in various physiological processes and patho-physiological conditions. The endogeneous TSPO ligand is a polypeptide of 9 kDa, but dipeptides with biological activity have been previously synthesized and characterized. Herein, we synthesized a phenyl alanine derived ligand with a ¹⁹F labelling which opens prospective for ¹⁹F-MRI and potential ¹⁸F-PET applications. We characterized the coexistence of two conformers that are not equally sensitive to the media used for membrane protein studies. Interaction studies with the recombinant mouse TSPO (mTSPO) in different membrane-mimicking environments are presented using ¹⁹F NMR enabling structure/function characterizations. A change in the mTSPO environment from pure detergent to lipid/detergent mixture reveals different exchange rates between bound and free ligand forms. Competition experiments with the high-affinity drug ligand (R)-PK 11195 suggests that phenyl alanine derived ligand binds in the same protein cavity.