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 sequenc e of botulinum toxin A were used as tools to identify an ion channel-f orming motif. A peptide denoted BoTxATM, with the sequence GAVILLEFIPE IAI PVLGTFALV, forms cation-selective channels when reconstituted in p lanar lipid bilayers. As predicted, the self-assembled conductive olig omers express heterogeneous single-channel conductances. The most freq uent 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 n ot formed by a peptide of the same amino acid composition as BoTxATM w ith 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 t hat the identified module may play a functional role in the ion channe l-forming activity of intact botulinum toxin A.