Mechanism of ammonia transport by Amt/MEP/Rh: structure of AmtB at 1.35 A |
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| Authors: | Khademi Shahram O'Connell Joseph Remis Jonathan Robles-Colmenares Yaneth Miercke Larry J W Stroud Robert M |
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| Institution: | Department of Biochemistry and Biophysics, S412C Genentech Hall, University of California-San Francisco, 600 16th Street, San Francisco, CA 94143-2240, USA. |
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| 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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