The charge state of an ion channel controls neutral polymer entry into its pore |
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Authors: | Sergey M Bezrukov John J Kasianowicz |
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Institution: | (1) National Institutes of Health, Division of Computing Research and Technology, 5/405, Bethesda, MD 20892, USA, US;(2) St. Petersburg Nuclear Physics Institute, Gatchina 188350, Russia, RU;(3) National Institutes of Standards and Technology, Biotechnology Division, Biomolecular Materials Group, 222/A353, Gaithersburg, MD 20899, USA, US |
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Abstract: | Electrostatic potentials created by fixed or induced charges regulate many cellular phenomena including the rate of ion transport
through proteinaceous ion channels. Nanometer-scale pores of these channels also play a critical role in the transport of
charged and neutral macromolecules. We demonstrate here that, surprisingly, changing the charge state of a channel markedly
alters the ability of nonelectrolyte polymers to enter the channel's pore. Specifically, we show that the partitioning of differently-sized linear nonelectrolyte
polymers of ethylene glycol into the Staphylococcus aureus α-hemolysin channel is altered by the solution pH. Protonating some of the channel side chains decreases the characteristic
polymer size (molecular weight) that can enter the pore by ∼25% but increases the ionic current by ∼15%. Thus, the “steric”
and “electric” size of the channel change in opposite directions. The results suggest that effects due to polymer and channel
hydration are crucial for polymer transport through such pores.
Received: 16 March 1997 / Accepted: 24 April 1997 |
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Keywords: | Ion channel Transport Polymers Hydration Water structure Alpha hemolysin Poly(ethylene glycol) |
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