Neutralization of a single arginine residue gates open a two-pore domain, alkali-activated K+ channel.
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.
Niemeyer
María Isabel
MI
Centro de Estudios Científicos, Avenida Arturo Prat 514, Valdivia 509-9100, Chile. miniemeyer@cecs.cl
González-Nilo
Fernando D
FD
Zúñiga
Leandro
L
González
Wendy
W
Cid
L Pablo
LP
Sepúlveda
Francisco V
FV
D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D024683:Potassium Channels, Tandem Pore Domain / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
C423407:KCNK17 protein, human; C498739:Kcnk5 protein, mouse; D024683:Potassium Channels, Tandem Pore Domain; D011994:Recombinant Proteins; D001120:Arginine