Abstract
A selectivity filter is a gate in ion channels that is responsible for the selection and fast conduction of particular ions across the membrane (with high throughput rates of 108 ions s−1 and a high 1:104 discrimination rate between ions). It is made of four strands as the backbone, and each strand is composed of sequences of five amino acids connected by peptide units H–N–C=O in which the main molecules in the backbone that interact with ions in the filter are carbonyl (C=O) groups that mimic the transient interactions of ion with binding sites during ion conduction. It has been suggested that quantum coherence and possible emergence of resonances in the backbone carbonyl groups may play a role in mediating ion conduction and selectivity in the filter. Here, we investigate the influence of noise and disorder on the efficiency of excitation energy transfer (EET) in a linear harmonic chain of N = 5 sites with dipole–dipole couplings as a simple model for one P-loop strand of the selectivity filter backbone in biological ion channels. We include noise and disorder inherent in real biological systems by including spatial disorder in the chain, and random noise within a weak coupling quantum master equation approach. Our results show that disorder in the backbone considerably reduces EET, but the addition of noise helps to recover high EET for a wide range of system parameters. Our analysis may help for better understanding of the coordination of ions in the filter as well as the fast and efficient functioning of the selectivity filters in ion channels.
Highlights
Excitation Energy Transfer (EET) has been recently investigated as one of the most important problems in physical and biological systems, e.g. in photosynthesis 1–6, charge transfer in DNA7 or motional excitation in α-helix structures.[8,9] Noise and disorder are inherent factors in energy transfer (EET) in biological and complex systems and they originate from various types of internal and external sources and affect the system dynamics
It has been suggested that quantum coherence and possible emergence of resonances in the backbone carbonyl groups may play a role in mediating ion conduction and selectivity in the filter
It has been suggested that quantum coherence and its interplay with thermal vibrations might be involved in mediating ion selectivity and transport[22]
Summary
Excitation Energy Transfer (EET) has been recently investigated as one of the most important problems in physical and biological systems, e.g. in photosynthesis 1–6, charge transfer in DNA7 or motional excitation in α-helix structures.[8,9] Noise and disorder are inherent factors in EET in biological and complex systems and they originate from various types of internal and external sources and affect the system dynamics. Recent studies have indicated that disorder and noise can enhance EET in some cases. This is in contrast to the standard scenario in quantum mechanical systems where strong enough disorder leads to localization of the wave functions[11] and vanishing of the related transport coefficient. It has been shown that disorder increases EET in a symmetric network because of invariant disconnected subspaces[10], or complex networks suffering from localization[11,13]. Disorder can optimize transport efficiency of a chromosphere inside a sphere[14,15,16]. Energy transport efficiency enhancement has been observed due to disorder on site energies in Ref. 17
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