title: Fluorescence detection of the movement of single KcsA subunits reveals cooperativity.
abstract: The prokaryotic KcsA channel is gated at the helical bundle crossing by intracellular protons and inactivates at the extracellular selectivity filter. The C-terminal transmembrane helix has to undergo a conformational change for potassium ions to access the central cavity. Whereas a partial opening of the tetrameric channel is suggested to be responsible for subconductance levels of ion channels, including KcsA, a cooperative opening of the 4 subunits is postulated as the final opening step. In this study, we used single-channel fluorescence spectroscopy of KcsA to directly observe the movement of each subunit and the temporal correlation between subunits. Purified KcsA channels labeled at the C terminus near the bundle crossing have been inserted into supported lipid bilayer, and the fluorescence traces analyzed by means of a cooperative or independent Markov model. The analysis revealed that the 4 subunits do not move fully independently but instead showed a certain degree of cooperativity. However, the 4 subunits do not simply open in 1 concerted step.
authors.affiliation: Département de Physique and GEPROM, Université de Montréal, Montréal, QC, Canada H3C 3J7. rikard.blunck@umontreal.ca
authors.forename: Rikard
authors.initials: R
authors.lastname: Blunck
authors.forename: Hugo
authors.initials: H
authors.lastname: McGuire
authors.forename: H Clark
authors.initials: HC
authors.lastname: Hyde
authors.forename: Francisco
authors.initials: F
authors.lastname: Bezanilla
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers; D008390:Markov Chains; D009038:Motion; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism*; D021122:Protein Subunits; D013050:Spectrometry, Fluorescence / Q000379:methods*
chemical_list: D001426:Bacterial Proteins; D008051:Lipid Bilayers; D015221:Potassium Channels; D021122:Protein Subunits; C107790:prokaryotic potassium channel