Beschreibung:
<jats:p>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 NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> transport in two archetypal members of the family, the transporters AmtB from <jats:italic>Escherichia coli</jats:italic> and Rh50 from <jats:italic>Nitrosomonas europaea</jats:italic>. The pathway underpins a mechanism by which charged H<jats:sup>+</jats:sup> and neutral NH<jats:sub>3</jats:sub> are carried separately across the membrane after NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> deprotonation. This mechanism defines a new principle of achieving transport selectivity against competing ions in a biological transport process.</jats:p>