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Ion Channels of Alamethicin Dimer N-Terminally Linked by Disulfide Bond

Takashi Okazaki ^*, Machiko Sakoh ^*, Yasuo Nagaoka  and Koji Asami ^*

^* Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; and Department of Biotechnology, Kansai University, Suita, Osaka 564-8680, Japan

Correspondence: Address reprint requests to Dr. Koji Asami, Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan. Tel.: +81-774-38-3081; Fax: +81-774-38-3084; E-mail: asami{at}tampopo.kuicr.kyoto-u.ac.jp.

A covalent dimer of alamethicin Rf30 was synthesized by linking the N-termini by a disulfide bond. When the dimer peptides were added to the cis-side of a diphytanoyl PC membrane, macroscopic channel current was induced only at cis positive voltages. The single-channel recordings showed several conductance levels that were alternately stabilized. These results indicate that the dimer peptides form stable channels by N-terminal insertion like alamethicin and that most of the pores are assembled from even numbers of helices. Taking advantages of the long open duration of the dimer peptide channels, the current-voltage (I-V) relations of the single-channels were obtained by applying fast voltage ramps during the open states. The I-V relations showed rectification, such that current from the cis-side toward the trans-side is larger than that in the opposite direction. The intrinsic rectification is mainly attributed to the macro dipoles of parallel peptide helices surrounding a central pore.

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