Application of photoaffinity crosslinking in determining the interaction between calcitonin and its receptor

Understanding the molecular mechanism underlying how the peptide ligands bind to their receptors with subsequent receptor activation and cellular response is of great long-term value in designing receptor-targeted drugs. This is more difficult for class-II G protein-coupled receptors as only minimal structural data is available and their natural peptide ligands contain a large and diffuse pharmacophore. To address this problem, photoaffinity labeling studies have been developed to identify the spatial proximity between the photophore-modified ligand and its receptor. This minireview looks at the application of this approach in determining the proximal sites between class-II G protein-coupled receptor peptide ligands and their corresponding receptors, including parathyroid hormone, secretin and vasoactive intestinal polypeptide. More specifically, we will highlight interaction sites between positions 19, 16 and 26 of calcitonin with C ¹³⁴ -K ¹⁴¹ , and F ¹³⁷ and T ³⁰ of the receptor, respectively.