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  Role of Bundle Helices in a Regulatory Crosstalk in the Trimeric Betaine Transporter BetP

Gärtner, R. M., Perez, C., Koshy, C., & Ziegler, C. (2011). Role of Bundle Helices in a Regulatory Crosstalk in the Trimeric Betaine Transporter BetP. Journal of Molecular Biology, 414(3), 327-336. doi:10.1016/j.jmb.2011.10.013.

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 Creators:
Gärtner, Rebecca M.1, Author           
Perez, Camilo1, Author           
Koshy, Caroline1, Author           
Ziegler, Christine1, Author           
Affiliations:
1Department of Structural Biology, Max Planck Institute of Biophysics, Max Planck Society, ou_2068291              

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Free keywords: alternating access; betaine transport; inverted repeats; Na+ coupling; transport activity regulation
 Abstract: The Na+-coupled betaine symporter BetP regulates transport activity in response to hyperosmotic stress only in its trimeric state, suggesting a regulatory crosstalk between individual protomers. BetP shares the overall fold of two inverted structurally related five-transmembrane (TM) helix repeats with the sequence-unrelated Na+-coupled symporters LeuT, vSGLT, and Mhp1, which are neither trimeric nor regulated in transport activity. Conformational changes characteristic for this transporter fold involve the two first helices of each repeat, which form a four-TM-helix bundle. Here, we identify two ionic networks in BetP located on both sides of the membrane that might be responsible for BetP's unique regulatory behavior by restricting the conformational flexibility of the four-TM-helix bundle. The cytoplasmic ionic interaction network links both first helices of each repeat in one protomer to the osmosensing C-terminal domain of the adjacent protomer. Moreover, the periplasmic ionic interaction network conformationally locks the four-TM-helix bundle between the same neighbor protomers. By a combination of site-directed mutagenesis, cross-linking, and betaine uptake measurements, we demonstrate how conformational changes in individual bundle helices are transduced to the entire bundle by specific inter-helical interactions. We suggest that one purpose of bundle networking is to assist crosstalk between protomers during transport regulation by specifically modulating the transition from outward-facing to inward-facing state.

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Language(s): eng - English
 Dates: 2011-10-042011-05-162011-10-112011-10-152011-12-02
 Publication Status: Published in print
 Pages: 10
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1016/j.jmb.2011.10.013
PMID: 22024596
 Degree: -

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Title: Journal of Molecular Biology
  Other : JMB
  Abbreviation : J. Mol. Biol.
Source Genre: Journal
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Publ. Info: Elsevier
Pages: - Volume / Issue: 414 (3) Sequence Number: - Start / End Page: 327 - 336 Identifier: ISSN: 0022-2836
CoNE: https://pure.mpg.de/cone/journals/resource/0022-2836