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  A channel profile report of the unusual K+ channel KtrB

Mikušević, V., Schrecker, M., Kolesova, N., Patiño-Ruiz, M., Fendler, K., & Hänelt, I. (2019). A channel profile report of the unusual K+ channel KtrB. Journal of General Physiology, 151. doi:10.1085/jgp.201912384.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0004-F631-F Version Permalink: http://hdl.handle.net/21.11116/0000-0004-F632-E
Genre: Journal Article

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 Creators:
Mikušević, Vedrana1, Author
Schrecker, Marina1, Author
Kolesova, Natalie1, Author
Patiño-Ruiz, Miyer2, Author              
Fendler, Klaus2, Author              
Hänelt, Inga1, Author
Affiliations:
1Institute of Biochemistry, Goethe University Frankfurt, Frankfurt, Germany, ou_persistent22              
2Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society, ou_persistent22              

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 Abstract: KtrAB is a key player in bacterial K+ uptake required for K+ homeostasis and osmoadaptation. The system is unique in structure and function. It consists of the K+-translocating channel subunit KtrB, which forms a dimer in the membrane, and the soluble regulatory subunit KtrA, which attaches to the cytoplasmic side of the dimer as an octameric ring conferring Na+ and ATP dependency to the system. Unlike most K+ channels, KtrB lacks the highly conserved T(X)GYG selectivity filter sequence. Instead, only a single glycine residue is found in each pore loop, which raises the question of how selective the ion channel is. Here, we characterized the KtrB subunit from the Gram-negative pathogen Vibrio alginolyticus by isothermal titration calorimetry, solid-supported membrane-based electrophysiology, whole-cell K+ uptake, and ACMA-based transport assays. We found that, despite its simple selectivity filter, KtrB selectively binds K+ with micromolar affinity. Rb+ and Cs+ bind with millimolar affinities. However, only K+ and the poorly binding Na+ are efficiently translocated, based on size exclusion by the gating loop. Importantly, the physiologically required K+ over Na+ selectivity is provided by the channel's high affinity for potassium, which interestingly results from the presence of the sodium ions themselves. In the presence of the KtrA subunit, sodium ions further decrease the Michaelis-Menten constant for K+ uptake from milli- to micromolar concentrations and increase the Vmax, suggesting that Na+ also facilitates channel gating. In conclusion, high binding affinity and facilitated K+ gating allow KtrAB to function as a selective K+ channel.

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Language(s): eng - English
 Dates: 2019-09-032019-04-182019-09-272019-10-17
 Publication Status: Published online
 Pages: 12
 Publishing info: -
 Table of Contents: -
 Rev. Method: Peer
 Identifiers: DOI: 10.1085/jgp.201912384
BibTex Citekey: mikusevic_channel_2019
 Degree: -

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Title: Journal of General Physiology
  Other : J. Gen. Physiol.
  Abbreviation : JGP
Source Genre: Journal
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Publ. Info: Rockefeller University Press
Pages: - Volume / Issue: 151 Sequence Number: - Start / End Page: - Identifier: ISSN: 0022-1295
CoNE: https://pure.mpg.de/cone/journals/resource/954925413895