Proton Movement and Coupling in the POT Family of Peptide Transporters

Proc Natl Acad Sci U S A. 2017 Dec 12;114(50):13182-13187. doi: 10.1073/pnas.1710727114. Epub 2017 Nov 27.

Abstract

POT transporters represent an evolutionarily well-conserved family of proton-coupled transport systems in biology. An unusual feature of the family is their ability to couple the transport of chemically diverse ligands to an inwardly directed proton electrochemical gradient. For example, in mammals, fungi, and bacteria they are predominantly peptide transporters, whereas in plants the family has diverged to recognize nitrate, plant defense compounds, and hormones. Although recent structural and biochemical studies have identified conserved sites of proton binding, the mechanism through which transport is coupled to proton movement remains enigmatic. Here we show that different POT transporters operate through distinct proton-coupled mechanisms through changes in the extracellular gate. A high-resolution crystal structure reveals the presence of ordered water molecules within the peptide binding site. Multiscale molecular dynamics simulations confirm proton transport occurs through these waters via Grotthuss shuttling and reveal that proton binding to the extracellular side of the transporter facilitates a reorientation from an inward- to outward-facing state. Together these results demonstrate that within the POT family multiple mechanisms of proton coupling have likely evolved in conjunction with variation of the extracellular gate.

Keywords: biophysics; major facilitator superfamily; membrane transport; peptide transport; proton movement.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Binding Sites
  • Membrane Transport Proteins / chemistry*
  • Membrane Transport Proteins / metabolism
  • Molecular Dynamics Simulation
  • Peptides / metabolism*
  • Protein Binding
  • Protons*
  • Xanthomonas / chemistry
  • Xanthomonas / metabolism

Substances

  • Bacterial Proteins
  • Membrane Transport Proteins
  • Peptides
  • Protons

Associated data

  • PDB/6EI3