Abbreviations. Bombyx mori L-Glutamate-gated chloride channel, BmGluCl; Bombyx mori γ-aminobutyric acid-gated chloride channel, BmGABACl; third transmembrane (TM3) Abstract Okaramines produced by Penicillium simplicissimum AK-40 activate L-glutamate-gated chloride channels (GluCls) and thus paralyze insects. However, the okaramine binding site on insect GluCls is poorly understood. Sequence alignment shows that the equivalent of residue Leucine319 of the okaramine B sensitive Bombyx mori GluCl

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... s a phenylalanine in the okaramine B insensitive B. mori γ-aminobutyric acid-gated chloride channel (BmGABACl) of the same species. This residue is located in the third transmembrane (TM3) region, a location which in a nematode GluCl is close to the ivermectin binding site. The B. mori GluCl containing the L319F mutation retained its sensitivity to L-glutamate, but responses to ivermectin were reduced and those to okaramine B were completely blocked.