eLife (Jul 2020)

A two-lane mechanism for selective biological ammonium transport

  • Gordon Williamson,
  • Giulia Tamburrino,
  • Adriana Bizior,
  • Mélanie Boeckstaens,
  • Gaëtan Dias Mirandela,
  • Marcus G Bage,
  • Andrei Pisliakov,
  • Callum M Ives,
  • Eilidh Terras,
  • Paul A Hoskisson,
  • Anna Maria Marini,
  • Ulrich Zachariae,
  • Arnaud Javelle

DOI
https://doi.org/10.7554/eLife.57183
Journal volume & issue
Vol. 9

Abstract

Read online

The transport of charged molecules across biological membranes faces the dual problem of accommodating charges in a highly hydrophobic environment while maintaining selective substrate translocation. This has been the subject of a particular controversy for the exchange of ammonium across cellular membranes, an essential process in all domains of life. Ammonium transport is mediated by the ubiquitous Amt/Mep/Rh transporters that includes the human Rhesus factors. Here, using a combination of electrophysiology, yeast functional complementation and extended molecular dynamics simulations, we reveal a unique two-lane pathway for electrogenic NH4+ transport in two archetypal members of the family, the transporters AmtB from Escherichia coli and Rh50 from Nitrosomonas europaea. The pathway underpins a mechanism by which charged H+ and neutral NH3 are carried separately across the membrane after NH4+ deprotonation. This mechanism defines a new principle of achieving transport selectivity against competing ions in a biological transport process.

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