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From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
Published on: July 4, 2016
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Crystal structure of a nitrate/nitrite exchanger
Hongjin Zheng1, Goragot Wisedchaisri, Tamir Gonen
1Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, Virginia 20147, USA.
Nature
|May 14, 2013
Summary
Researchers determined the structure of a bacterial nitrate/nitrite transporter, NarK. This finding reveals how nitrate and nitrite are exchanged across cell membranes, elucidating a key nitrogen metabolism process.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Nitrate is a key mineral nitrogen source for microorganisms.
- Nitrate assimilation involves reduction to nitrite, which can be toxic if accumulated.
- The transport mechanism of nitrate remains largely unknown due to a lack of structural data.
Purpose of the Study:
- To determine the structure of a bacterial nitrate/nitrite transporter, NarK, from Escherichia coli.
- To elucidate the mechanism of nitrate and nitrite transport.
Main Methods:
- X-ray crystallography was used to obtain structures of NarK with and without substrate.
- Mutagenesis and functional studies were performed to identify key residues.
Main Results:
- The crystal structures revealed a positively charged substrate-translocation pathway.
- Conserved arginine residues form the substrate-binding pocket.
- NarK functions as a nitrate/nitrite exchanger, likely via a rocker switch mechanism.
Conclusions:
- The NarK structure provides insights into the mechanism of nitrate/nitrite exchange.
- Proton co-transport is unlikely in NarK function.
- Identified key residues are crucial for substrate recognition and transport.
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