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Ion Permeation by a Folded Multiblock Amphiphilic Oligomer Achieved by Hierarchical Construction of Self-Assembled Nanopores

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posted on 05.12.2012, 00:00 authored by Takahiro Muraoka, Tatsuya Shima, Tsutomu Hamada, Masamune Morita, Masahiro Takagi, Kazuhito V. Tabata, Hiroyuki Noji, Kazushi Kinbara
A multiblock amphiphilic molecule 1, with a tetrameric alternating sequence of hydrophilic and hydrophobic units, adopts a folded structure in a liposomal membrane like a multipass transmembrane protein, and is able to transport alkali metal cations through the membrane. Hill’s analysis and conductance measurements, analyzed by the Hille equation, revealed that the tetrameric assembly of 1 forms a 0.53 nm channel allowing for permeation of cations. Since neither 3, bearing flexible hydrophobic units and forming no stacked structures in the membrane, nor 2, a monomeric version of 1, is able to transport cations, the folded conformation of 1 in the membrane is likely essential for realizing its function. Thus, function and hierarchically formed higher-order structures of 1, is strongly correlated with each other like proteins and other biological macromolecules.