Nicotinic acetylcholine receptors (nAChRs) are pharmaceutical targets for diseases such as Alzheimer’s, nicotine addiction and lung cancer¹. Despite immense clinical efforts for over 20 years, only one drug, varenicline, has been approved for smoking cessation¹. This challenge in nAChR-based research stems from the lack of subtype-selective research probes, which limits the characterisation of the functional diversity of the nAChR subtypes¹. The conesnail venom is an evolution-driven combinatorial library of disulphide-rich peptides - conotoxins, which are developed for defence and prey capture. These peptides are designed to target a range of ion channels in the nervous system, inducing paralysis within seconds of envenomation². A subset of these conotoxins called α-conotoxins target the nAChRs with nanomolar affinity and exhibit some subtype selectivity³. Using structure activity relationship (SAR) studies, it is possible to further develop these peptides into invaluable molecular probes with improved selectivity and affinity at specific nAChR subtypes. 

α-Conotoxin LsIA was discovered and characterised from the crude venom of Conus limpusi⁴. LsIA is an equipotent (10 nM) antagonist of both α7 and α3β2 subtypes⁴. SAR studies of LsIA revealed novel features of the peptide influencing selectivity between the α7 and α3β2 nAChR subtypes⁴. To gain further insight into the specific receptor-ligand interactions co-ordinating the selective binding of LsIA at these subtypes, we co-crystallised LsIA with Lymnaea stagnalis acetylcholine binding protein (AChBP), a homologue of the nAChR ligand binding domain. The 2.8Å crystal structure highlights a network of receptor-ligand interactions in which LsIA Arg10 and Asn12 play a key role. The structure defines novel selectivity determinants between the α7, α3β2 and the α3β4 nAChRs that will be used in the rational design of selective probes for these clinically important nAChR subtypes.