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Biophys J, July 2002, p. 219-228, Vol. 83, No. 1

Modifications of Alamethicin Ion Channels by Substitution of Glu-7 for Gln-7

Koji Asami,* Takashi Okazaki,* Yasuaki Nagai,* and Yasuo Nagaokadagger

 *Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; and  dagger Faculty of Pharmaceutical Science, Kyoto University, Sakyo-ku, Kyoto 606-0001, Japan

To evaluate the role of charged residues facing a pore lumen in stability of channel structure and ion permeation, we studied electrical properties of ion channels formed by synthesized native alamethicins (Rf50 (alm-Q7Q18) and Rf30 (alm-Q7E18)) and their analogs with Glu-7 (alm-E7Q18 and alm-E7E18). The single-channel currents were measured over a pH range of 3.5 to 8.7 using planar bilayers of diphytanoyl PC. The peptides all showed multi-level current fluctuations in this pH range. At pH 3.5 the channels formed by the four peptides were similar to each other irrespective of the side chain differences at positions 7 and 18. The ionization of Glu-7 (E7) and Glu-18 (E18) above neutral pH reduced the relative probabilities of low-conductance states (levels 1 and 2) and increased those of high-conductance states (levels 4-6). The channel conductance of the peptides with E7 and/or E18, which was distinct from that of alm-Q7Q18, showed a marked pH-dependence, especially for low-conductance states. The ionization of E7 further reduced the stability of channel structure, altered the current-voltage curve from a superlinear relation to a sublinear one, and enhanced cation selectivity. These results indicate that ionized E7 strongly influences the channel structure and the ion permeation, in contrast to ionized E18.

Biophys J, July 2002, p. 219-228, Vol. 83, No. 1
© 2002 by the Biophysical Society   0006-3495/02/07/219/10  $2.00


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T. Okazaki, M. Sakoh, Y. Nagaoka, and K. Asami
Ion Channels of Alamethicin Dimer N-Terminally Linked by Disulfide Bond
Biophys. J., July 1, 2003; 85(1): 267 - 273.
[Abstract] [Full Text] [PDF]


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