Identification of novel allosteric modulators of the glycine receptor using phage display technology

The glycine receptor (GlyR) is a ligand-gated ion channel and a member of the cys-loop receptor family. Like other members of this family, the GlyR is a target for many drugs of abuse, including alcohol. While the effects of alcohol on these receptors have been well-characterized, the contribution of each receptor subtype to the overall physiological and behavioral effects of alcohol use are unclear. This is partially due to the limited pharmacology of the GlyR, which limits the ability to isolate GlyR function within a complex system. One method for identifying compounds that bind to and modulate a given target is phage display. This approach uses bacteriophage to screen a large number of peptide sequences for affinity at a given target. We developed a phage selection protocol to identify peptides that bind to the GlyR. These peptides were then tested for functional effects at the GlyR using two-electrode voltage clamp physiology. We identified several peptides that were able to modulate GlyR function. Peptide D12-116 showed specificity for the GlyR over two closely related γ-aminobutyric acid (GABA) channels. In addition, this method is easily adapted for the selection of peptides that bind to any cell-expressed target, increasing the utility of phage display in the neurobiology field. Another shortcoming in GlyR pharmacology is the lack of modulators with specificity for a single GlyR subtype. We next adjusted our selection protocol to search for peptides that can distinguish between the different Gly R α subtypes. We identified several promising lead peptides that show subtype preference. Finally, we found that trifluoroacetic acid (TFA), a common peptide contaminant, also modulates GlyR function. This finding has important implications for both previously reported peptide modulators and the pharmacology of several volatile anesthetics, for which TFA is the major metabolite