title: Quantitative analysis of the water occupancy around the selectivity filter of a K+ channel in different gating modes.
abstract: Recovery in K(+) channels, that is, the transition from the inactivated nonconductive selectivity filter conformation toward the conductive conformation, occurs on a time scale of the order of seconds, which is astonishingly long, given that the structural differences among the filter conformations are faint (<1 Å). Computational studies and electrophysiological measurements suggested that buried water molecules bound behind the selectivity filter are at the origin of the slowness of recovery in K(+) channels. Using a combination of solid-state NMR spectroscopy (ssNMR) and long molecular dynamics simulations, we sketch a high-resolution map of the spatial and temporal distribution of water behind the selectivity filter of a membrane-embedded K(+) channel in two different gating modes. Our study demonstrates that buried water molecules with long residence times are spread all along the rear of the inactivated filter, which explains the recovery kinetics. In contrast, the same region of the structure appears to be dewetted when the selectivity filter is in the conductive state. Using proton-detected ssNMR on fully protonated channels, we demonstrate the presence of a pathway that allows for the interchange of buried and bulk water, as required for a functional influence of buried water on recovery and slow inactivation. Furthermore, we provide direct experimental evidence for the presence of additional ordered water molecules that surround the filter and that are modulated by the channel's gating mode.
authors.affiliation: NMR Spectroscopy, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University , 3584 CH Utrecht, The Netherlands.
authors.forename: Markus
authors.initials: M
authors.lastname: Weingarth
authors.forename: Elwin A W
authors.initials: EA
authors.lastname: van der Cruijsen
authors.forename: Jared
authors.initials: J
authors.lastname: Ostmeyer
authors.forename: Sylke
authors.initials: S
authors.lastname: Lievestro
authors.forename: Benoît
authors.initials: B
authors.lastname: Roux
authors.forename: Marc
authors.initials: M
authors.lastname: Baldus
mesh_terms: D019295:Computational Biology / Q000379:methods*; D015640:Ion Channel Gating; D056004:Molecular Dynamics Simulation; D019906:Nuclear Magnetic Resonance, Biomolecular; D015221:Potassium Channels / Q000737:chemistry*; D011487:Protein Conformation; D014867:Water / Q000737:chemistry*
chemical_list: D015221:Potassium Channels; D014867:Water