Inhibition of Neuronal Nicotinic Acetylcholine Receptor Subtypes by α-Conotoxin GID and Analogues

alpha-Conotoxins are small disulfide-rich peptides from the venom of the Conus species that target the nicotinic acetylcholine receptor (nAChR). They are valuable pharmacological tools and also have potential therapeutic applications particularly for the treatment of chronic pain. alpha-Conotoxin GID is isolated from the venom of Conus geographus and has an unusual N-terminal tail sequence that has been shown to be important for binding to the alpha 4 beta 2 subtype of the nAChR. To date, only four conotoxins that inhibit the alpha 4 beta 2 subtype have been characterized, but they are of considerable interest as it is the most abundant nAChR subtype in the mammalian brain and has been implicated in a range of diseases. In this study, analysis of alaninescan and truncation mutants of GID reveals that a conserved proline in alpha-conotoxins is important for activity at the alpha 7, alpha 3 beta 2, and alpha 4 beta 2 subtypes. Although the proline residue was the most critical residue for activity at the alpha 3 beta 2 subtype, Asp3, Arg12, and Asn14 are also critical at the alpha 7 subtype. Interestingly, very few of the mutations tested retained activity at the alpha 4 beta 2 subtype indicating a tightly defined binding site. This lack of tolerance to sequence variation may explain the lack of selective ligands discovered for the alpha 4 beta 2 subtype to date. Overall, our findings contribute to the understanding of the structureactivity relationships of alpha-conotoxins and may be beneficial for the ongoing attempts to exploit modulators of the neuronal nAChRs as therapeutic agents.