Isolation and characterization of alpha-conotoxin LsIA with potent activity at nicotinic acetylcholine receptors

A new a-conotoxin LsIA was isolated from the crude venom of Conus limpusi using assay-guided RP-HPLC fractionation. Synthetic LsIA was a potent antagonist of a3ß2, a3a5ß2 and a7 nAChRs, with half-maximal inhibitory concentrations of 10, 31 and 10 nM, respectively. The structure of LsIA determined by NMR spectroscopy comprised a characteristic disulfide bond-stabilized a-helical structure and disordered N-terminal region. Potency reductions of up to 9-fold were observed for N-terminally truncated analogues of LsIA at a7 and a3ß2 nAChRs, whereas C-terminal carboxylation enhanced potency 3-fold at a3ß2 nAChRs but reduced potency 3-fold at a7 nAChRs. This study gives further insight into a-conotoxin pharmacology and the molecular basis of nAChR selectivity, highlighting the influence of N-terminal residues and C-terminal amidation on conotoxin pharmacology.