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  Crystal structure of an ammonia-permeable aquaporin.

Kirscht, A., Kaptan, S. S., Bienert, G. P., Chaumont, F., Nissen, P., de Groot, B. L., et al. (2016). Crystal structure of an ammonia-permeable aquaporin. PLOS Biology, 14(3): e1002411. doi:10.1371/journal.pbio.1002411.

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Kirscht, A., Author
Kaptan, S. S.1, Author           
Bienert, G. P., Author
Chaumont, F., Author
Nissen, P., Author
de Groot, B. L.1, Author           
Kjellbom, P., Author
Gourdon, P., Author
Johanson, U., Author
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1Research Group of Computational Biomolecular Dynamics, MPI for Biophysical Chemistry, Max Planck Society, ou_578573              

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 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 angstrom 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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Language(s): eng - English
 Dates: 2016-03-30
 Publication Status: Published online
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 Rev. Type: Peer
 Identifiers: DOI: 10.1371/journal.pbio.1002411
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Title: PLOS Biology
Source Genre: Journal
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Pages: 19 Volume / Issue: 14 (3) Sequence Number: e1002411 Start / End Page: - Identifier: -