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. 2004 Sep 10;305(5690):1587-94.
doi: 10.1126/science.1101952.

Mechanism of ammonia transport by Amt/MEP/Rh: structure of AmtB at 1.35 A

Shahram Khademi  1 , Joseph O'Connell 3rd, Jonathan Remis, Yaneth Robles-Colmenares, Larry J W Miercke, Robert M Stroud
Affiliations

Mechanism of ammonia transport by Amt/MEP/Rh: structure of AmtB at 1.35 A

Shahram Khademi et al. Science. .

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.

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