Ammonium Transporters Achieve Charge Transfer by Fragmenting Their Substrate

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• 作者：Shihao Wang ; Esam A. Orabi ; Sefer Baday ; Simon Bern猫che ; Guillaume Lamoureux
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：June 27, 2012
• 年：2012
• 卷：134
• 期：25
• 页码：10419-10427
• 全文大小：446K
• 年卷期：v.134,no.25(June 27, 2012)
• ISSN：1520-5126

文摘

Proteins of the Amt/MEP family facilitate ammonium transport across the membranes of plants, fungi, and bacteria and are essential for growth in nitrogen-poor environments. Some are known to facilitate the diffusion of the neutral NH₃, while others, notably in plants, transport the positively charged NH₄⁺. On the basis of the structural data for AmtB from Escherichia coli, we illustrate the mechanism by which proteins from the Amt family can sustain electrogenic transport. Free energy calculations show that NH₄⁺ is stable in the AmtB pore, reaching a binding site from which it can spontaneously transfer a proton to a pore-lining histidine residue (His168). The substrate diffuses down the pore in the form of NH₃, while the excess proton is cotransported through a highly conserved hydrogen-bonded His168鈥揌is318 pair. This constitutes a novel permeation mechanism that confers to the histidine dyad an essential mechanistic role that was so far unknown.