Role of the Gln/Glu residues of trichocellins A-II/B-II in ion-channel formation in lipid membranes and catecholamine secretion from chromaffin cells

Abstract

Trichocellins (TC) A-II and B-II, 20-residue peptaibols isolated from conidia of the fungus Trichoderma viride, have the same sequence except for the residue at position 18. Both TCs were found to form voltage-dependent ion-channels in bilayer lipid membranes (BLM) and to induce catecholamine secretion from bovine adrenal chromaffin cells through Ca 2+ influx. TC-A-II (Gln 18, neutral) was more effective than TC-B-II (Glu 18, charged) for macroscopic current induction in BLMs and for catecholamine secretion from chromaffin cells, suggesting that Glu 18 is unfavorable for the ion-channel formation in BLMs and chromaffin cell membranes. Nevertheless, single-channel recordings indicated that TC-B-II forms larger pores with longer open lifetimes than those of TC-A-II. This indicates that the negatively charged carboxyl group of Glu at position 18 stabilizes larger pores. The effects of the negative charge of Glu 18 on the activities were confirmed by the use of a TC-B-II analog containing the methyl ester of Glu 18.