FORMATION OF ION CHANNELS IN LIPID BILAYERS BY A PEPTIDE WITH THE PREDICTED TRANSMEMBRANE SEQUENCE OF BOTULINUM NEUROTOXIN-A

Synthetic peptides patterned after the predicted transmembrane sequence of botulinum toxin A were used as tools to identify an ion channel-forming motif. A peptide denoted BoTxATM, with the sequence GAVILLEFIPEIAI PVLGTFALV, forms cation-selective channels when reconstituted in planar lipid bilayers. As predicted, the self-assembled conductive oligomers express heterogeneous single-channel conductances. The most frequent openings exhibit single-channel conductance of 12 and 7 pS in 0.5 M NaCl, and 29 and 9 pS in 0.5 M KCl. In contrast, ion channels are not formed by a peptide of the same amino acid composition as BoTxATM with a scrambled sequence. Conformational energy calculations show that a bundle of four amphipathic alpha-helices is a plausible structural motif underlying the measured pore properties. These studies suggest that the identified module may play a functional role in the ion channel-forming activity of intact botulinum toxin A.