KcsA is a homotetrameric 68-kDa membrane-associated potassium channel which selectively gates the flux of potassium ions across the membrane. The channel is known to undergo a pH-dependent open-to-closed transition. Following a study of the intact tetrameric channel, we have carried out an NMR study of the monomeric subunit of the channel (KcsAM), solubilized in SDS micelles. Chemical shift, solvent exchange, backbone 15N relaxation and residual dipolar coupling (RDC) data show the TM1 helix to remain intact, but the TM2 helix contains a distinct kink, which is subject to concentration-independent but pH-dependent conformational exchange on a microsecond time scale. The kink region, centered at G99, was previously implicated in gating of the tetrameric KcsA channel. An RDC-based model of KcsAM at acidic pH orients TM1 and the two helical segments of the kinked TM2 in a configuration reminiscent of the open conformation of the channel. Thus, the transition between states appears to be an inherent capability of the monomer, with the tetrameric assembly exerting a modulatory effect upon the transition which gives the channel its physiological gating profile.

Project Start
Project End
Budget Start
Budget End
Support Year
24
Fiscal Year
2008
Total Cost
$101,643
Indirect Cost
City
State
Country
United States
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Lee, Jung Ho; Ying, Jinfa; Bax, Ad (2016) Quantitative evaluation of positive ? angle propensity in flexible regions of proteins from three-bond J couplings. Phys Chem Chem Phys 18:5759-70
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Chill, Jordan H; Louis, John M; Miller, Christopher et al. (2006) NMR study of the tetrameric KcsA potassium channel in detergent micelles. Protein Sci 15:684-98
Ying, Jinfa; Grishaev, Alexander; Bax, Ad (2006) Carbon-13 chemical shift anisotropy in DNA bases from field dependence of solution NMR relaxation rates. Magn Reson Chem 44:302-10

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