Vibrational excitons in ionophores: Experimental probes for quantum coherence-assisted ion transport and selectivity in ion channels

TL;DR

This paper proposes an experimental approach using time-resolved IR spectroscopy to investigate quantum coherence effects in ion transport within potassium channels, supported by simulations and model molecule studies.

Contribution

It introduces a novel experimental strategy combining IR spectroscopy and isotope labeling to probe quantum effects in ion channels, validated by molecular dynamics simulations.

Findings

IR and Raman signatures of potassium binding molecules identified

Feasibility demonstrated for observing potassium interactions with binding sites

Specific isotope labeling combinations predicted to enhance experimental detection

Abstract

Despite a large body of work, the exact molecular details underlying ion-selectivity and transport in the potassium channel have not been fully laid to rest. One major reason has been the lack of experimental methods that can probe these mechanisms dynamically on their biologically relevant time scales. Recently it was suggested that quantum coherence and its interplay with thermal vibration might be involved in mediating ion-selectivity and transport. In this work we present an experimental strategy for using time resolved infrared spectroscopy to investigate these effects. We show the feasibility by demonstrating the IR absorption and Raman spectroscopic signatures of potassium binding model molecules that mimic the transient interactions of potassium with binding sites of the selectivity filter during ion conduction. In addition to guide our experiments on the real system we have performed molecular dynamic-based simulations of the FTIR and 2DIR spectra of the entire KcsA complex, which is the largest complex for which such modeling has been performed. We found that by combing isotope labeling with 2D IR spectroscopy, the signatures of potassium interaction with individual binding sites would be experimentally observable and identified specific labeling combinations that would maximize our expected experimental signatures.