Interactions between histidine and tryptophan residues in the BM2 proton channel from influenza B virus

Area of Science:

• Virology
• Structural Biology
• Biophysics

Background:

• The BM2 protein of influenza B virus is crucial for viral infection, forming a transmembrane proton channel.
• Understanding the BM2 proton channel's structure and mechanism is key to developing antiviral strategies.

Purpose of the Study:

• To investigate the structure and mechanism of the BM2 proton channel using a peptide model (BM2-TMP).
• To elucidate the roles of specific amino acids (His19, Trp23, His27) in channel function and proton selectivity.

Main Methods:

• Utilized a 31-mer peptide (BM2-TMP) representing the BM2 transmembrane domain.
• Performed site-directed mutagenesis (His19-Ala, His27-Ala, Trp23-Phe) to assess channel activity.
• Employed biophysical techniques including Circular Dichroism (CD), fluorescence, and Raman spectroscopy across a range of pH values.

Main Results:

• BM2-TMP formed a pH-activated proton channel (midpoint pH 6.4), similar to the full-length protein.
• His19 is critical for channel activity; His27 contributes but is not essential.
• Trp23 substitution abolished proton selectivity, indicating its role in the proton gate.
• Identified a cation-pi interaction between His and Trp residues, crucial for channel gating below pH 6.5.

Conclusions:

• The His19-Trp23 cation-pi interaction is likely the trigger for BM2 proton channel opening.
• His27 enhances channel activity and, with Trp23, forms the proton-selective gate.
• These findings provide insights into the molecular mechanism of influenza B virus BM2 proton channel function.