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

Proton movement and coupling in the POT family of peptide transporters.

Author information

1
Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom; joanne.parker@bioch.ox.ac.uk jmswanson@uchicago.edu simon.newstead@bioch.ox.ac.uk.
2
Department of Chemistry, The University of Chicago, Chicago, IL 60637.
3
Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637.
4
James Franck Institute, The University of Chicago, Chicago, IL 60637.
5
School of Medicine, Trinity College Dublin, Dublin, Ireland.
6
School of Biochemistry and Immunology, Trinity College Dublin, Dublin, Ireland.
7
Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom.
8
Department of Chemistry, The University of Chicago, Chicago, IL 60637; joanne.parker@bioch.ox.ac.uk jmswanson@uchicago.edu simon.newstead@bioch.ox.ac.uk.

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

PMID:
29180426
PMCID:
PMC5740623
DOI:
10.1073/pnas.1710727114
[Indexed for MEDLINE]
Free PMC Article

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