title: Mechanism of formate-nitrite transporters by dielectric shift of substrate acidity.
abstract: Bacterial formate-nitrite transporters (FNTs) regulate the metabolic flow of small, weak mono-acids. Recently, the eukaryotic PfFNT was identified as the malaria parasite's lactate transporter and novel drug target. Despite crystal data, central mechanisms of FNT gating and transport remained unclear. Here, we show elucidation of the FNT transport mechanism by single-step substrate protonation involving an invariant lysine in the periplasmic vestibule. Opposing earlier gating hypotheses and electrophysiology reports, quantification of total uptake by radiolabeled substrate indicates a permanently open conformation of the bacterial formate transporter, FocA, irrespective of the pH Site-directed mutagenesis, heavy water effects, mathematical modeling, and simulations of solvation imply a general, proton motive force-driven FNT transport mechanism: Electrostatic attraction of the acid anion into a hydrophobic vestibule decreases substrate acidity and facilitates protonation by the bulk solvent. We define substrate neutralization by proton transfer for transport via a hydrophobic transport path as a general theme of the Amt/Mep/Rh ammonium and formate-nitrite transporters.
authors.affiliation: Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany.
authors.forename: Marie
authors.initials: M
authors.lastname: Wiechert
authors.affiliation: Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, Kiel, Germany ebeitz@pharmazie.uni-kiel.de.
authors.forename: Eric
authors.identifier: 0000-0001-5912-6626
authors.initials: E
authors.lastname: Beitz
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D005561:Formates / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008962:Models, Theoretical; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D009573:Nitrites / Q000378:metabolism*; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D005561:Formates; D026901:Membrane Transport Proteins; D009573:Nitrites; D015800:Protozoan Proteins; C030544:formic acid
keywords: formate–nitrite transporter; lactate; neutralization; proton transfer; transport mechanism