title: Ion-binding properties of a K+ channel selectivity filter in different conformations.
abstract: K(+) channels are membrane proteins that selectively conduct K(+) ions across lipid bilayers. Many voltage-gated K(+) (KV) channels contain two gates, one at the bundle crossing on the intracellular side of the membrane and another in the selectivity filter. The gate at the bundle crossing is responsible for channel opening in response to a voltage stimulus, whereas the gate at the selectivity filter is responsible for C-type inactivation. Together, these regions determine when the channel conducts ions. The K(+) channel from Streptomyces lividians (KcsA) undergoes an inactivation process that is functionally similar to KV channels, which has led to its use as a practical system to study inactivation. Crystal structures of KcsA channels with an open intracellular gate revealed a selectivity filter in a constricted conformation similar to the structure observed in closed KcsA containing only Na(+) or low [K(+)]. However, recent work using a semisynthetic channel that is unable to adopt a constricted filter but inactivates like WT channels challenges this idea. In this study, we measured the equilibrium ion-binding properties of channels with conductive, inactivated, and constricted filters using isothermal titration calorimetry (ITC). EPR spectroscopy was used to determine the state of the intracellular gate of the channel, which we found can depend on the presence or absence of a lipid bilayer. Overall, we discovered that K(+) ion binding to channels with an inactivated or conductive selectivity filter is different from K(+) ion binding to channels with a constricted filter, suggesting that the structures of these channels are different.
authors.affiliation: Department of Biology, Texas A&M University, College Station, TX 77843;
authors.forename: Shian
authors.initials: S
authors.lastname: Liu
authors.affiliation: Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239;
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Focke
authors.affiliation: Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239;
authors.forename: Kimberly
authors.initials: K
authors.lastname: Matulef
authors.affiliation: Department of Biology, Texas A&M University, College Station, TX 77843;
authors.forename: Xuelin
authors.initials: X
authors.lastname: Bian
authors.affiliation: Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health and Science University, Portland, OR 97239;
authors.forename: Pierre
authors.initials: P
authors.lastname: Moënne-Loccoz
authors.affiliation: Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239;
authors.forename: Francis I
authors.initials: FI
authors.lastname: Valiyaveetil
authors.affiliation: Department of Biology, Texas A&M University, College Station, TX 77843; Texas A&M Institute for Neuroscience, Texas A&M University, College Station, TX 77843 lockless@bio.tamu.edu.
authors.forename: Steve W
authors.initials: SW
authors.lastname: Lockless
mesh_terms: D003902:Detergents / Q000737:chemistry; D015640:Ion Channel Gating; D008051:Lipid Bilayers; D011188:Potassium / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation
chemical_list: D003902:Detergents; D008051:Lipid Bilayers; D011188:Potassium
keywords: K+ channel; electron paramagnetic resonance spectroscopy; inactivation; ion binding; isothermal titration calorimetry