Synthesis and testing of photoaffinity probes for the site-selective chemical modifications of the 5-HT3 receptor

The 5-HT3 receptor (5-HT3R) is an important ion channel responsible for the transmission of nerve impulses in the central nervous system.1 It is difficult to characterize transmembrane dynamic receptors with classical structural biology approaches like crystallization and x-ray. The use of photoaffinity probes is an alternative approach to identify regions in the protein that are important for the binding of small molecules. Therefore we synthesized a small library of photoaffinity probes by conjugating photophores via various linkers to granisetron which is a known antagonist of the 5-HT3R. We were able to obtain several compounds with diverse linker lengths and different photolabile moieties that show nanomolar binding affinities for the orthosteric binding site. Furthermore we established a stable h5-HT3R expressing cell line and a purification protocol to yield the receptor in a high purity. Currently we are investigating the photo crosslinking of these ligands with the 5-HT3R.