Abstract
The first structure of an ammonia channel from the Amt/MEP/Rh protein superfamily, determined to 1.35 angstrom resolution, shows it to be a channel that spans the membrane 11 times. Two structurally similar halves span the membrane with opposite polarity. Structures with and without ammonia or methyl ammonia show a vestibule that recruits NH4+/NH3, a binding site for NH4+, and a 20 angstrom-long hydrophobic channel that lowers the NH4+ pKa to below 6 and conducts NH3. Favorable interactions for NH3 are seen within the channel and use conserved histidines. Reconstitution of AmtB into vesicles shows that AmtB conducts uncharged NH3.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Ammonia / metabolism*
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Binding Sites
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Biological Transport
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Cation Transport Proteins / chemistry*
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Cation Transport Proteins / genetics
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Cation Transport Proteins / metabolism
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Cell Membrane / chemistry
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Crystallization
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Crystallography, X-Ray
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Escherichia coli / chemistry*
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Escherichia coli / metabolism
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Escherichia coli Proteins / chemistry*
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Escherichia coli Proteins / genetics
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Escherichia coli Proteins / metabolism
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Hydrogen Bonding
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Hydrogen-Ion Concentration
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Hydrophobic and Hydrophilic Interactions
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Liposomes
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Membrane Potentials
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Models, Molecular
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Molecular Sequence Data
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Protein Conformation
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Protein Folding
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Protein Structure, Quaternary
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Protein Structure, Secondary
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Quaternary Ammonium Compounds / metabolism
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Rh-Hr Blood-Group System / chemistry
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Rh-Hr Blood-Group System / metabolism
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Sequence Alignment
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Water / chemistry
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Water / metabolism
Substances
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AmtB protein, E coli
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Cation Transport Proteins
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Escherichia coli Proteins
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Liposomes
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Quaternary Ammonium Compounds
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Rh-Hr Blood-Group System
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Water
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Ammonia
Associated data
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PDB/1U77
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PDB/1U7C
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PDB/1U7G