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J Gen Physiol. 2016 Aug;148(2):119-32. doi: 10.1085/jgp.201611602. Epub 2016 Jul 18.

Conformational heterogeneity in closed and open states of the KcsA potassium channel in lipid bicelles.

Author information

1
Department of Anesthesiology, Weill Cornell Medical College, New York, NY 10065.
2
Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065.
3
Department of Anesthesiology, Weill Cornell Medical College, New York, NY 10065 Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY 10065.
4
Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065 Brain and Mind Research Institute, Weill Cornell Medical College, New York, NY 10065 crn2002@med.cornell.edu dae2005@med.cornell.edu.
5
Department of Anesthesiology, Weill Cornell Medical College, New York, NY 10065 Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065 Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY 10065 crn2002@med.cornell.edu dae2005@med.cornell.edu.

Abstract

The process of ion channel gating-opening and closing-involves local and global structural changes in the channel in response to external stimuli. Conformational changes depend on the energetic landscape that underlies the transition between closed and open states, which plays a key role in ion channel gating. For the prokaryotic, pH-gated potassium channel KcsA, closed and open states have been extensively studied using structural and functional methods, but the dynamics within each of these functional states as well as the transition between them is not as well understood. In this study, we used solution nuclear magnetic resonance (NMR) spectroscopy to investigate the conformational transitions within specific functional states of KcsA. We incorporated KcsA channels into lipid bicelles and stabilized them into a closed state by using either phosphatidylcholine lipids, known to favor the closed channel, or mutations designed to trap the channel shut by disulfide cross-linking. A distinct state, consistent with an open channel, was uncovered by the addition of cardiolipin lipids. Using selective amino acid labeling at locations within the channel that are known to move during gating, we observed at least two different slowly interconverting conformational states for both closed and open channels. The pH dependence of these conformations and the predictable disruptions to this dependence observed in mutant channels with altered pH sensing highlight the importance of conformational heterogeneity for KcsA gating.

PMID:
27432996
PMCID:
PMC4969796
DOI:
10.1085/jgp.201611602
[Indexed for MEDLINE]
Free PMC Article

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