Direct Evidence of Channel-Water Dynamics Related with the Structure Changes in a Transmembrane Ion Channel

Abstract

Knowledge of both structural and dynamical characteristics are essential to understand the function of membrane proteins. Two-dimensional infrared (2D IR) spectroscopy can detect small changes in secondary structure as well as measure fast structure dynamics on the picosecond timescale. Here, we report a 2D IR spectroscopic investigation to probe the backbone configurations of the transmembrane domain of M2 proton channel in a solid-supported membrane environment. Our results show that a helix kink at higher pH (7.5) occludes the passage of water molecules into the channel, making the channel inactive. A conformational change upon lowering the pH (5.5), shows ultrafast hydrogen-bond dynamics between the amide carbonyls of the transmembrane protein and the water molecules, confirming the presence of water inside the channel in the active state. This result suggests that the rate of proton diffusion is closely related to the water dynamics induced by the structural change in the protein.