Synthetic peptides with amino acid ~eqttences corresponding to predicted transmembran¢ segments of tet~tntts toxin were used as probes to identify a elmnnel-forming motif. A peptide denoted TeTx 1I. with sequence GVVLLLEYIPEITLPVIAALSIA, form.~ cation-selective channels when r~onztltuted in planar lipid bilaycrz. The .~ia~le channel conductance in 0.~ M NaCI or KCI is 28 + 3 ~tnd 24 ± 2 pS. respectively. In contrast, a peptide with sequence NFIGALETTGVVLLLEYIPEIT. denoted as TeTx I. or a peptide with the mine amino acid composition as TeTx II but with a randomized ~eqaence, do not form channels. Conformational enersy calculations show that a baladle of four amphipathic a-helices is a plausible structural motif underlying observable pore properties. The identified functional module may account for the channel-forming activity of both tetanus toxin ~md the hom~losous botulinum to~in A.
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