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Journal of Biochemistry Advance Access published online on January 20, 2009
Journal of Biochemistry, doi:10.1093/jb/mvp009
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© The authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Interactions between Histidine and Tryptophan Residues in the BM2 Proton Channel from Influenza B Virus

Kohei Otomo, Akira Toyama{ddagger}, Takashi Miura and Hideo Takeuchi*

Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan

*To whom correspondence should be addressed: Hideo Takeuchi: Tel: +81-22-795-6855, Fax: +81-22-795-6855, E-mail: takeuchi{at}mail.tains.tohoku.ac.jp

Received December 16, 2008; Accepted January 10, 2009


  Abstract

The BM2 protein of influenza B virus forms a transmembrane proton channel essential for the virus infection. We investigated the structure and mechanism of the BM2 proton channel by using a 31-mer peptide (BM2-TMP) representing the putative transmembrane domain of BM2, with special focus on His19, Trp23, and His27. Like the full-length protein, BM2-TMP formed a transmembrane proton channel activated at acidic pH with a midpoint of transition at pH 6.4 ± 0.1. Mutation of His19 to Ala almost abolished the channel activity, whereas the His27-to-Ala mutant retained partial activity. The proton selectivity of the channel was lost upon substitution of Phe for Trp23. Comparison of CD, fluorescence, and Raman spectra measured for wild-type and mutated BM2-TMP at varied pH showed the pKa of the imidazole ring to be ~6.5 for His19 and ~7.6 for His27. Analysis of the pH-dependent fluorescence and Raman intensities suggested the occurrence of cation-{pi} interaction between the protonated imidazole ring of His and the indole ring of Trp. The His19-Trp23 cation-{pi} interaction below pH 6.5 is likely to trigger the opening of the proton channel, whereas His27 is not essential but enhances the channel activity through interaction with Trp23, which constitutes the proton-selective gate.

Key Words: cation-{pi} interaction, histidine, influenza virus, proton channel, tryptophan

{ddagger} Present address: Division of Pharmacy, Medical and Dental Hospital, Niigata University, 1-754 Asahimachi-dori, Niigata 951-8520, Japan.


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