Characterization of a Novel α-Conotoxin from Conus textile That Selectively Targets α6/α3β2β3 Nicotinic Acetylcholine Receptors

alpha 6 beta 2 Nicotinic acetylcholine receptors (nAChRs) expressed by dopaminergic neurons in the CNS are potential therapeutic targets for the treatment of several neuropsychiatric diseases, including nicotine addiction and Parkinson disease. However, recent studies indicate that the alpha 6 subunit can also associate with the beta 4 subunit to form alpha 6 beta 4 nAChRs that are difficult to pharmacologically distinguish from alpha 6 beta 2, alpha 3 beta 4, and alpha 3 beta 2 subtypes. The current study characterized a novel 16-amino acid alpha-conotoxin (alpha-CTx) TxIB from Conus textile whose sequence is GCCSDPPCRNKHPDLC-amide as deduced from gene cloning. The peptide and an analog with an additional C-terminal glycine were chemically synthesized and tested on rat nAChRs heterologously expressed in Xenopus laevis oocytes. alpha-CTx TxIB blocked alpha 6/alpha 3 beta 2 beta 3 nAChR with an IC50 of 28 nM. In contrast, the peptide showed little or no block of other tested subtypes at concentrations up to 10 mu M. The three-dimensional solution structure of alpha-CTx TxIB was determined using NMR spectroscopy. alpha-CTx TxIB represents a uniquely selective ligand for probing the structure and function of alpha 6 beta 2 nAChRs.