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Crystal Structure of an Ammonia-Permeable Aquaporin

Kirscht, Andreas LU ; Kaptan, Shreyas S.; Bienert, Gerd Patrick; Chaumont, François; Nissen, Poul; de Groot, Bert L.; Kjellbom, Per LU ; Gourdon, Pontus LU and Johanson, Urban LU (2016) In PLoS Biology 14(3).
Abstract

Aquaporins of the TIP subfamily (Tonoplast Intrinsic Proteins) have been suggested to facilitate permeation of water and ammonia across the vacuolar membrane of plants, allowing the vacuole to efficiently sequester ammonium ions and counteract cytosolic fluctuations of ammonia. Here, we report the structure determined at 1.18 Å resolution from twinned crystals of Arabidopsis thaliana aquaporin AtTIP2;1 and confirm water and ammonia permeability of the purified protein reconstituted in proteoliposomes as further substantiated by molecular dynamics simulations. The structure of AtTIP2;1 reveals an extended selectivity filter with the conserved arginine of the filter adopting a unique unpredicted position. The relatively wide pore and the... (More)

Aquaporins of the TIP subfamily (Tonoplast Intrinsic Proteins) have been suggested to facilitate permeation of water and ammonia across the vacuolar membrane of plants, allowing the vacuole to efficiently sequester ammonium ions and counteract cytosolic fluctuations of ammonia. Here, we report the structure determined at 1.18 Å resolution from twinned crystals of Arabidopsis thaliana aquaporin AtTIP2;1 and confirm water and ammonia permeability of the purified protein reconstituted in proteoliposomes as further substantiated by molecular dynamics simulations. The structure of AtTIP2;1 reveals an extended selectivity filter with the conserved arginine of the filter adopting a unique unpredicted position. The relatively wide pore and the polar nature of the selectivity filter clarify the ammonia permeability. By mutational studies, we show that the identified determinants in the extended selectivity filter region are sufficient to convert a strictly water-specific human aquaporin into an AtTIP2;1-like ammonia channel. A flexible histidine and a novel water-filled side pore are speculated to deprotonate ammonium ions, thereby possibly increasing permeation of ammonia. The molecular understanding of how aquaporins facilitate ammonia flux across membranes could potentially be used to modulate ammonia losses over the plasma membrane to the atmosphere, e.g., during photorespiration, and thereby to modify the nitrogen use efficiency of plants.

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organization
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publication status
published
subject
in
PLoS Biology
volume
14
issue
3
publisher
Public Library of Science
external identifiers
  • scopus:84962170580
  • wos:000373038200025
ISSN
1544-9173
DOI
10.1371/journal.pbio.1002411
language
English
LU publication?
yes
id
242078c0-227e-43ed-a71c-ede4e7c6554f
date added to LUP
2016-09-19 10:01:40
date last changed
2017-10-08 04:52:24
@article{242078c0-227e-43ed-a71c-ede4e7c6554f,
  abstract     = {<p>Aquaporins of the TIP subfamily (Tonoplast Intrinsic Proteins) have been suggested to facilitate permeation of water and ammonia across the vacuolar membrane of plants, allowing the vacuole to efficiently sequester ammonium ions and counteract cytosolic fluctuations of ammonia. Here, we report the structure determined at 1.18 Å resolution from twinned crystals of Arabidopsis thaliana aquaporin AtTIP2;1 and confirm water and ammonia permeability of the purified protein reconstituted in proteoliposomes as further substantiated by molecular dynamics simulations. The structure of AtTIP2;1 reveals an extended selectivity filter with the conserved arginine of the filter adopting a unique unpredicted position. The relatively wide pore and the polar nature of the selectivity filter clarify the ammonia permeability. By mutational studies, we show that the identified determinants in the extended selectivity filter region are sufficient to convert a strictly water-specific human aquaporin into an AtTIP2;1-like ammonia channel. A flexible histidine and a novel water-filled side pore are speculated to deprotonate ammonium ions, thereby possibly increasing permeation of ammonia. The molecular understanding of how aquaporins facilitate ammonia flux across membranes could potentially be used to modulate ammonia losses over the plasma membrane to the atmosphere, e.g., during photorespiration, and thereby to modify the nitrogen use efficiency of plants.</p>},
  articleno    = {e1002411},
  author       = {Kirscht, Andreas and Kaptan, Shreyas S. and Bienert, Gerd Patrick and Chaumont, François and Nissen, Poul and de Groot, Bert L. and Kjellbom, Per and Gourdon, Pontus and Johanson, Urban},
  issn         = {1544-9173},
  language     = {eng},
  month        = {03},
  number       = {3},
  publisher    = {Public Library of Science},
  series       = {PLoS Biology},
  title        = {Crystal Structure of an Ammonia-Permeable Aquaporin},
  url          = {http://dx.doi.org/10.1371/journal.pbio.1002411},
  volume       = {14},
  year         = {2016},
}