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Water permeation across artificial I-quartet membrane channels: from structure to disorder

Abstract

Aquaporins allow fast water transport across membranes (~108-109 water molecules/s/channel), with complete exclusion of ions thanks to an hourglass structure with a narrowest constriction of 2.8 Å. Few synthetic channels have been designed to mimic this high water permeability, and none reject ions at a significant level. Recent works on designed self-assembling alkylureido-ethylimidazole compounds forming imidazole-quartet channels (I-quartets), have shown high water permeability across lipid bilayers and total ionic-rejection [1]. I-quartets are promising candidates for further development of artificial water channels (AWC). However the molecular mechanism of water permeation as well as I-quartet organization and stability in a membrane environment need to be fully understood to guide optimal AWC design. Here, we use a wide range of all-atom molecular dynamics (MD) simulations to understand the structure/activity relationships of the artificial I-quartet water channels. Four different I-quartet channels with varying alkyl chain length or chirality have been studied in a complex fully hydrated lipid bilayer environment at both microsecond and nanosecond scale. Microsecond simulations shows two distinct behaviors; (i) two out of four of the self-assembled I-quartets embedded within lipid bilayers maintain chiral dipolar oriented water wires, but also undergo strong reorganization of the crystal shape, (ii) the two other I-quartets channels completely lose the crystal packing organization, nonetheless keeping a water transport activity. Short MD simulations with higher time resolution were conducted to characterize the dynamic properties of water molecules in these model channels and provided a detailed hypothesis on the molecular mechanism of water transport. The ordered confined water was characterized with quantitative measures of hydrogen-bond life-time and single particle dynamics, showing discrepancy within I-quartets channels. We will further discuss the underlying assumptions, currently based on self-aggregation simulations and crystal patches embedded in lipid bilayer simulations and attempt to describe possible alternative approaches to computationally capture the water permeation mechanism and the self-assembly process of these AWC. [1] Licsandru et al. JACS (2016), 138(16), 5403-5409.

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Publication details

The article was received on 24 Feb 2018, accepted on 27 Apr 2018 and first published on 02 May 2018


Article type: Paper
DOI: 10.1039/C8FD00046H
Citation: Faraday Discuss., 2018, Accepted Manuscript
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    Water permeation across artificial I-quartet membrane channels: from structure to disorder

    S. Murail, T. Vasiliu, A. Neamtu, M. D. Barboiu, F. Sterpone and M. Baaden, Faraday Discuss., 2018, Accepted Manuscript , DOI: 10.1039/C8FD00046H

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