Fluorescence detection of the movement of single KcsA subunits reveals cooperativity.
Proc Natl Acad Sci U S A
; 105(51): 20263-8, 2008 Dec 23.
Article
em En
| MEDLINE
| ID: mdl-19074286
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.
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Base de dados:
MEDLINE
Assunto principal:
Espectrometria de Fluorescência
/
Proteínas de Bactérias
/
Canais de Potássio
Idioma:
En
Ano de publicação:
2008
Tipo de documento:
Article