Dynamic control of protein structure by cation-π interaction

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We have studied the effects of interaction between a positive charge and π electrons, i.e. cation-π interaction, on the structural formation and dynamics of proteins by circular dichroism (CD), fluorescence, and UV resonance Raman spectroscopy. The peptides and proteins studied are neuromedin B, neuromedin C, and the transmembrane region of influenza B virus BM2 protein (BM2-TMP). The cation-π interaction between His^+ and Trp was found to be unable to control the secondary structures of neuromedin B and C, suggesting that such cation-π interactions do not so much contribute to protein structural stability. However, analogous cation-π interactions play an important role in gating a proton channel formed by BM2-TMP in lipid bilayers, demonstrating that cation-π interactions can control the functioning of a protein by modifying its local structure near functionally important regions. In addition, cation-π interaction between Cu^<2+> and Trp was found to cause not only a shift and intensity change of UV absorption of the Trp indole ring but also to generate a negative signal in CD spectra. The negative CD signal is expected to serve as a new marker of cation-π interaction between Cu^<2+> and Trp in proteins. As shown in the case of the proton channel formed by BM2-TMP, cation-π interactions could play important roles in structural dynamics of proteins associated with their functioning. Although the present proposal about the role of cation-a interaction in protein functioning need to be further tested in many other proteins, the present study has provided the basis of such future studies.