1xqe: Difference between revisions

Revision as of 15:22, 3 May 2008

The mechanism of ammonia transport based on the crystal structure of AmtB of E. coli.

OverviewOverview

Ammonium is one of the most important nitrogen sources for bacteria, fungi, and plants, but it is toxic to animals. The ammonium transport proteins (methylamine permeases/ammonium transporters/rhesus) are present in all domains of life; however, functional studies with members of this family have yielded controversial results with respect to the chemical identity (NH(4)(+) or NH(3)) of the transported species. We have solved the structure of wild-type AmtB from Escherichia coli in two crystal forms at 1.8- and 2.1-A resolution, respectively. Substrate transport occurs through a narrow mainly hydrophobic pore located at the center of each monomer of the trimeric AmtB. At the periplasmic entry, a binding site for NH(4)(+) is observed. Two phenylalanine side chains (F107 and F215) block access into the pore from the periplasmic side. Further into the pore, the side chains of two highly conserved histidine residues (H168 and H318) bridged by a H-bond lie adjacent, with their edges pointing into the cavity. These histidine residues may facilitate the deprotonation of an ammonium ion entering the pore. Adiabatic free energy calculations support the hypothesis that an electrostatic barrier between H168 and H318 hinders the permeation of cations but not that of the uncharged NH(3.) The structural data and energetic considerations strongly indicate that the methylamine permeases/ammonium transporters/rhesus proteins are ammonia gas channels. Interestingly, at the cytoplasmic exit of the pore, two different conformational states are observed that might be related to the inactivation mechanism by its regulatory partner.

About this StructureAbout this Structure

1XQE is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.

ReferenceReference

The mechanism of ammonia transport based on the crystal structure of AmtB of Escherichia coli., Zheng L, Kostrewa D, Berneche S, Winkler FK, Li XD, Proc Natl Acad Sci U S A. 2004 Dec 7;101(49):17090-5. Epub 2004 Nov 24. PMID:15563598 Page seeded by OCA on Sat May 3 15:22:06 2008

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OCA

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 [[Image:1xqe.gif|left|200px]]
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-|RESOURCES=<span class='plainlinks'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1xqe FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1xqe OCA], [http://www.ebi.ac.uk/pdbsum/1xqe PDBsum], [http://www.rcsb.org/pdb/explore.do?structureId=1xqe RCSB]</span>
-}}
 '''The mechanism of ammonia transport based on the crystal structure of AmtB of E. coli.'''
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 [[Category: Winkler, F K.]]
 [[Category: Zheng, L.]]
-[[Category: ammonia transport]]
+[[Category: Ammonia transport]]
-[[Category: open conformation]]
+[[Category: Open conformation]]
-[[Category: wild type]]
+[[Category: Wild type]]
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May  3 15:22:06 2008''
-''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Mar 31 00:53:13 2008''