Nicotinic acetylcholine receptors: α-conotoxins as templates for rational drug design

Nicotinic acetylcholine receptors (nAChRs) mediate the passage of potassium and sodium ions across synaptic membranes. Two classes of receptors exist: the neuromuscular nAChRs, which mediate signals between nerve and muscle cells, and the neuronal nAChRs, which are found throughout the nervous system. For treatment of diseases involving nAChRs, drugs must be designed with a high level of selectivity towards only one of these classes or subclasses (in the case of neuronal receptors). α-Conotoxins, small polypeptides isolated from the venoms of marine snails, represent molecules with just this type of selectivity, with specificity even towards certain subclasses of nAChRs. The availability of high-resolution crystal structures of α-conotoxins provides the opportunity to examine the structural features that orchestrate their preferential blocking action. In the present study of a neuromuscular- and a neuronal-specific α-conotoxin, SI and EpI respectively, important and significant differences can be seen in the shapes of the molecules, which must reflect topological features of the different types of target receptor subunits. These then provide a template for computational docking studies with the homologous acetylcholine-binding protein, whose structure is known, so drug analogues of the naturally occurring toxins can be developed with the desired specificities.