Neutralization of a single arginine residue gates open a two-pore domain, alkali-activated K⁺ channel

• Published in: Proceedings of the National Academy of Sciences - PNAS 2007-01, Vol.104 (2), p.666-671
• Main Authors: Niemeyer, María Isabel, González-Nilo, Fernando D, Zúñiga, Leandro, González, Wendy, Cid, L. Pablo, Sepúlveda, Francisco V
• Format: Article
• Language: English
• Subjects: Alkalinity; Amino Acid Sequence; Amino acids; Animals; Arginine - chemistry; Basic amino acids; Biological Sciences; Electric potential; Electrical potential; Electrostatics; Humans; Hydrogen-Ion Concentration; In Vitro Techniques; Ion Channel Gating; Ions; Mice; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Patch clamp techniques; Potassium; Potassium Channels, Tandem Pore Domain - chemistry; Potassium Channels, Tandem Pore Domain - genetics; Potassium Channels, Tandem Pore Domain - metabolism; Protein Conformation; Proteins; Protons; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Sensors; Sequence Homology, Amino Acid; Simulation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0606173104

Potassium channels share a common selectivity filter that determines the conduction characteristics of the pore. Diversity in K⁺ channels is given by how they are gated open. TASK-2, TALK-1, and TALK-2 are two-pore region (2P) KCNK K⁺ channels gated open by extracellular alkalinization. We have explored the mechanism for this alkalinization-dependent gating using molecular simulation and site-directed mutagenesis followed by functional assay. We show that the side chain of a single arginine residue (R224) near the pore senses pH in TASK-2 with an unusual pKa of 8.0, a shift likely due to its hydrophobic environment. R224 would block the channel through an electrostatic effect on the pore, a situation relieved by its deprotonation by alkalinization. A lysine residue in TALK-2 fulfills the same role but with a largely unchanged pKa, which correlates with an environment that stabilizes its positive charge. In addition to suggesting unified alkaline pH-gating mechanisms within the TALK subfamily of channels, our results illustrate in a physiological context the principle that hydrophobic environment can drastically modulate the pKa of charged amino acids within a protein.