3C1J

Substrate binding, deprotonation and selectivity at the periplasmic entrance of the E. coli ammonia channel AmtB


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2 Å
  • R-Value Free: 0.210 
  • R-Value Work: 0.181 

wwPDB Validation 3D Report Full Report


This is version 1.2 of the entry. See complete history

Literature

Substrate binding, deprotonation, and selectivity at the periplasmic entrance of the Escherichia coli ammonia channel AmtB.

Javelle, A.Lupo, D.Ripoche, P.Fulford, T.Merrick, M.Winkler, F.K.

(2008) Proc.Natl.Acad.Sci.Usa 105: 5040-5045

  • DOI: 10.1073/pnas.0711742105
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 
  • The conduction mechanism of Escherichia coli AmtB, the structurally and functionally best characterized representative of the ubiquitous Amt/Rh family, has remained controversial in several aspects. The predominant view has been that it facilitates t ...

    The conduction mechanism of Escherichia coli AmtB, the structurally and functionally best characterized representative of the ubiquitous Amt/Rh family, has remained controversial in several aspects. The predominant view has been that it facilitates the movement of ammonium in its uncharged form as indicated by the hydrophobic nature of a pore located in the center of each subunit of the homotrimer. Using site-directed mutagenesis and a combination of biochemical and crystallographic methods, we have investigated mechanistic questions concerning the putative periplasmic ammonium ion binding site S1 and the adjacent periplasmic "gate" formed by two highly conserved phenylalanine residues, F107 and F215. Our results challenge models that propose that NH(4)(+) deprotonation takes place at S1 before NH(3) conduction through the pore. The presence of S1 confers two critical features on AmtB, both essential for its function: ammonium scavenging efficiency at very low ammonium concentration and selectivity against water and physiologically important cations. We show that AmtB activity absolutely requires F215 but not F107 and that removal or obstruction of the phenylalanine gate produces an open but inactive channel. The phenyl ring of F215 must thus play a very specific role in promoting transfer and deprotonation of substrate from S1 to the central pore. We discuss these results with respect to three distinct mechanisms of conduction that have been considered so far. We conclude that substrate deprotonation is an essential part of the conduction mechanism, but we do not rule out net electrogenic transport.


    Organizational Affiliation

    Biomolecular Research, Paul Scherrer Institut, CH-5232 Villigen, Switzerland.




Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
Ammonia channel
A
424Escherichia coli (strain K12)Mutation(s): 2 
Gene Names: amtB (ybaG)
Find proteins for P69681 (Escherichia coli (strain K12))
Go to UniProtKB:  P69681
Small Molecules
Ligands 3 Unique
IDChainsName / Formula / InChI Key2D Diagram3D Interactions
ACT
Query on ACT

Download SDF File 
Download CCD File 
A
ACETATE ION
C2 H3 O2
QTBSBXVTEAMEQO-UHFFFAOYSA-M
 Ligand Interaction
GOL
Query on GOL

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Download CCD File 
A
GLYCEROL
GLYCERIN; PROPANE-1,2,3-TRIOL
C3 H8 O3
PEDCQBHIVMGVHV-UHFFFAOYSA-N
 Ligand Interaction
IMD
Query on IMD

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Download CCD File 
A
IMIDAZOLE
C3 H5 N2
RAXXELZNTBOGNW-UHFFFAOYSA-O
 Ligand Interaction
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2 Å
  • R-Value Free: 0.210 
  • R-Value Work: 0.181 
  • Space Group: P 63
Unit Cell:
Length (Å)Angle (°)
a = 110.230α = 90.00
b = 110.230β = 90.00
c = 84.642γ = 120.00
Software Package:
Software NamePurpose
XSCALEdata scaling
MOLREPphasing
MAR345data collection
REFMACrefinement
XDSdata reduction

Structure Validation

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Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2008-03-18
    Type: Initial release
  • Version 1.1: 2011-07-13
    Type: Non-polymer description, Version format compliance
  • Version 1.2: 2017-10-25
    Type: Refinement description