title: Novel insights into the structural basis of pH-sensitivity in inward rectifier K+ channels Kir2.3.
abstract: The Kir2 channels belong to a family of potassium selective channels with characteristic strong inward rectification. Heteromeric assemblies of Kir2.1, Kir2.2 and Kir2.3 channels underly membrane potential stabilizing currents in ventricular myocytes, neurons and skeletal muscle. Kir2 channels differ substantially in their sensitivity to extracellular pH. The extracellular histidine Kir2.3(H117) contributes to the pH dependence of K-channels containing Kir2.3. Here, we study the possibility of intramolecular interactions of the residue Kir2.3(H117) with conserved cysteines in close proximity to the selectivity filter. We engineered a cobalt coordination site and reduction/oxidation sensitivity in Kir2.3 by introduction of a cysteine into the putatively hydrogen bonding residue (Kir2.3(H117C)) confirming that this residue is in proximity to Kir2.3(C141). Using SCAM we determined the location of the Kir2.3(H117) in the outer pore mouth and incorporated these data into a 3D model. We conclude that formation of a hydrogen bond at low pH may stabilize the outer pore domain to favour the selectivity filter in a slightly distorted conformation thus reducing ion permeation. The data provide molecular insight into the unique pH regulation of inward rectifier channels.
authors.affiliation: Physiology I, University of Tuebingen, Germany.
authors.forename: Oana N
authors.initials: ON
authors.lastname: Ureche
authors.forename: Ravshan
authors.initials: R
authors.lastname: Baltaev
authors.forename: Liviu
authors.initials: L
authors.lastname: Ureche
authors.forename: Nathalie
authors.initials: N
authors.lastname: Strutz-Seebohm
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
authors.forename: Guiscard
authors.initials: G
authors.lastname: Seebohm
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003035:Cobalt / Q000494:pharmacology; D004220:Disulfides / Q000378:metabolism; D004594:Electrophysiology; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D014982:Xenopus laevis
chemical_list: D004220:Disulfides; C099489:KCNJ4 protein, human; D024661:Potassium Channels, Inwardly Rectifying; D003035:Cobalt