title: Interactions between histidine and tryptophan residues in the BM2 proton channel from influenza B virus.
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 pK(a) of the imidazole ring to be approximately 6.5 for His19 and approximately 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.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Otomo
authors.forename: Akira
authors.initials: A
authors.lastname: Toyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Miura
authors.forename: Hideo
authors.initials: H
authors.lastname: Takeuchi
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D005453:Fluorescence; D006639:Histidine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D009981:Influenza B virus / Q000737:chemistry*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D011522:Protons; D017386:Sequence Homology, Amino Acid; D013059:Spectrum Analysis, Raman; D013329:Structure-Activity Relationship; D013997:Time Factors; D014364:Tryptophan / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C064964:BM2 polypeptide, influenza B virus; D007473:Ion Channels; D008081:Liposomes; D050505:Mutant Proteins; D011522:Protons; D014764:Viral Proteins; D006639:Histidine; D014364:Tryptophan