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J Biol Chem. 2015 Oct 30;290(44):26765-75. doi: 10.1074/jbc.M115.661819. Epub 2015 Sep 14.

Pore hydration states of KcsA potassium channels in membranes.

Author information

1
From the Institute for Bioscience and Biotechnology Research, University of Maryland, Rockville, Maryland 20850.
2
the Department of Physiology and Biophysics, University of California, Irvine, California 92697, the National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, Maryland 20899.
3
the Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland 20892.
4
the Physics Department, University of Massachusetts, Amherst, Massachusetts 01003, and From the Institute for Bioscience and Biotechnology Research, University of Maryland, Rockville, Maryland 20850.
5
From the Institute for Bioscience and Biotechnology Research, University of Maryland, Rockville, Maryland 20850, emihailescu@ibbr.umd.edu.

Abstract

Water-filled hydrophobic cavities in channel proteins serve as gateways for transfer of ions across membranes, but their properties are largely unknown. We determined water distributions along the conduction pores in two tetrameric channels embedded in lipid bilayers using neutron diffraction: potassium channel KcsA and the transmembrane domain of M2 protein of influenza A virus. For the KcsA channel in the closed state, the distribution of water is peaked in the middle of the membrane, showing water in the central cavity adjacent to the selectivity filter. This water is displaced by the channel blocker tetrabutyl-ammonium. The amount of water associated with the channel was quantified, using neutron diffraction and solid state NMR. In contrast, the M2 proton channel shows a V-shaped water profile across the membrane, with a narrow constriction at the center, like the hourglass shape of its internal surface. These two types of water distribution are therefore very different in their connectivity to the bulk water. The water and protein profiles determined here provide important evidence concerning conformation and hydration of channels in membranes and the potential role of pore hydration in channel gating.

KEYWORDS:

KcsA; M2; influenza virus; ion channels; lipid bilayer; neutron diffraction; nuclear magnetic resonance (NMR); potassium channel

PMID:
26370089
PMCID:
PMC4646329
DOI:
10.1074/jbc.M115.661819
[Indexed for MEDLINE]
Free PMC Article

Publication type, MeSH terms, Substances, Secondary source ID, Grant support

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