Structure and mechanism of the Mrp complex, an ancient cation/proton antiporter

Elife. 2020 Jul 31;9:e59407. doi: 10.7554/eLife.59407.


Multiple resistance and pH adaptation (Mrp) antiporters are multi-subunit Na+ (or K+)/H+ exchangers representing an ancestor of many essential redox-driven proton pumps, such as respiratory complex I. The mechanism of coupling between ion or electron transfer and proton translocation in this large protein family is unknown. Here, we present the structure of the Mrp complex from Anoxybacillus flavithermus solved by cryo-EM at 3.0 Å resolution. It is a dimer of seven-subunit protomers with 50 trans-membrane helices each. Surface charge distribution within each monomer is remarkably asymmetric, revealing probable proton and sodium translocation pathways. On the basis of the structure we propose a mechanism where the coupling between sodium and proton translocation is facilitated by a series of electrostatic interactions between a cation and key charged residues. This mechanism is likely to be applicable to the entire family of redox proton pumps, where electron transfer to substrates replaces cation movements.

Keywords: anoxybacillus flavithermus; antiporter; membrane transport; molecular biophysics; proton pump; respiratory complex I; structural biology.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anoxybacillus / metabolism*
  • Antiporters / metabolism*
  • Antiporters / ultrastructure
  • Bacterial Proteins / metabolism*
  • Bacterial Proteins / ultrastructure
  • Biological Transport, Active
  • Cations / metabolism
  • Cryoelectron Microscopy
  • Escherichia coli
  • Models, Molecular
  • Multiprotein Complexes / metabolism
  • Multiprotein Complexes / ultrastructure
  • Protein Conformation
  • Protons
  • Sodium / metabolism


  • Antiporters
  • Bacterial Proteins
  • Cations
  • Multiprotein Complexes
  • Protons
  • Sodium

Supplementary concepts

  • Anoxybacillus flavithermus