title: Activation-coupled inactivation in the bacterial potassium channel KcsA.
abstract: X-ray structures of the bacterial K+ channel KcsA have led to unparalleled progress in our understanding of ion channel structures. The KcsA channel has therefore been a prototypic model used to study the structural basis of ion channel function, including the gating mechanism. This channel was previously found to close at near-neutral intracellular pH (pH(i)) and to open at acidic pH(i). Here, we report the presence of a previously unknown channel inactivation process that occurs after the KcsA channel is activated. In our experiments, mammalian cells transfected with a codon-optimized synthetic gene encoding the KcsA protein expressed K+-selective channels that activated in response to a decrease in pH(i). Using patch-clamp and rapid solution exchange techniques, we observed that the KcsA channels inactivated within hundreds of milliseconds after channel activation. At all tested pHs, inactivation always accompanied activation, and it was profoundly accelerated in the same pH range at which activation increased steeply. Recovery from inactivation was observed, and its extent depended on the pH(i) and the amount of time that the channel was inactive. KcsA channel inactivation can be described by a kinetic model in which pH(i) controls inactivation through pH-dependent activation. This heretofore-undocumented inactivation process increases the complexity of KcsA channel function, but it also offers a potential model for studying the structural correspondence of ion channel inactivation.
authors.affiliation: Department of Physiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Lizhi
authors.initials: L
authors.lastname: Gao
authors.forename: Xianqiang
authors.initials: X
authors.lastname: Mi
authors.forename: Vesa
authors.initials: V
authors.lastname: Paajanen
authors.forename: Kun
authors.initials: K
authors.lastname: Wang
authors.forename: Zheng
authors.initials: Z
authors.lastname: Fan
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002522:Chlorocebus aethiops; D004594:Electrophysiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D048170:Streptomyces lividans / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D015221:Potassium Channels; C107790:prokaryotic potassium channel