THz trapped ion model and THz spectroscopy detection of potassium channels

Advanced molecular dynamics (MD) simulation and infrared (IR) spectroscopy have been widely adopted to reveal the detailed dynamic process of high-speed selective permeability of potassium channels. Yet these MD simulations cannot avoid the choice of empirical molecular force fields and high transmembrane voltages (as driving electric fields for ions) far exceeding physiological levels. Moreover, the IR spectroscopy method usually requires isotope labels for carbonyl groups of the channels, which may change the original permeation process. Here, we build the terahertz (THz) trapped ion model for the selectivity filter (SF) of potassium channels KcsA based on the density functional theory (DFT) calculation of ion potentials. In this model, the zero-point energy of trapped ions and quantum tunneling effect provide the physical basis for near diffusion limited permeation rates of ions and explain the high driving electric field in MD simulations. Quantitative calculations of zero-point energy and tunneling probability show that the quantum effect assisted knock-on mechanism may help to realize the physiological functions of potassium channels. Furthermore, based on the trapped ion model, we calculated the ion decoherence timescale under the influence of protein environmental noise. We use the quantum optics method to describe the interaction between THz waves and the trapped ion. Then the novel THz spectroscopy approaches through the THz resonance fluorescence and the intense field non-resonant effect are presented theoretically. These are expected to be isotope label-free detective methods of the rapid ion permeation dynamics.