The venoms of marine gastropods of the Conus genus contain a particularly wide array of bioactive peptides that inhibit nicotinic acetylcholine receptor (nAChR) activity, known as α-conotoxins. Many members of this family display remarkable selectivity and potency for specific neuronal nAChR subtypes and have provided an enormous repertoire of pharmacological probes for characterisation of receptor function and as analgesic drug leads. The 16-amino acid α-conotoxin Vc1.1, originally identified from the cDNA of Conus victoriae, displays potent and prolonged analgesic activity in several rodent models of neuropathic pain and significant efforts have been made to develop this molecule as a pharmacological treatment for chronic pain syndromes in humans.
We recently described a truncated analogue of Vc1.1, [Ser3]Vc1.1(1-8) (hereby referred to as Vc1.1(1-8)), entirely lacking the loop 2 residues and consisting of only the fully conserved loop 1 residues (GCSSDPRC), braced by the single Cys2-8 disulfide1. This miniaturised conotoxin analogue, Vc1.1(1-8) was able to inhibit >90% of α7 nAChR-mediated currents at a concentration of 1 µM1.
In this study, we investigated the structure/activity relationships of Vc1.1(1-8) at nAChRs by designing and synthesising a library of Vc1.1(1-8) analogues. We screened this library at nAChRs expressed in Xenopus oocytes to assess their pharmacological properties and to refine and optimise favourable structure-activity relationships of this minimal functional motif. Using this information, we have developed a small, stable and selective sub-nanomolar inhibitor of the α7 nAChR subtype that will be a valuable tool for understanding the physiological function of these receptors.