Ruyu Jia, Chloe Martens, Mrinal Shekhar, Shashank Pant, Grant Pellowe, Andy
Lau, Heather Findlay, Nicola Harris, Emad Tajkhorshid, Paula Booth, and
Argyris Politis.
Hydrogen-deuterium exchange mass spectrometry captures distinct
dynamics upon substrate and inhibitor binding to a transporter.
Nature Communications, 11, 2020.
(PMC: PMC7710758)
JIA2020-ET
Proton-coupled transporters use transmembrane proton gradients
to power active transport of nutrients inside the cell. High-
resolution structures often fail to capture the coupling between
proton and ligand binding, and conformational changes associated
with transport. We combine HDX-MS with mutagenesis and MD
simulations to dissect the molecular mechanism of the
prototypical transporter XylE. We show that protonation of a
conserved aspartate triggers conformational transition from
outward-facing to inward-facing state. This transition only
occurs in the presence of substrate xylose, while the inhibitor
glucose locks the transporter in the outward-facing state. MD
simulations corroborate the experiments by showing that only the
combination of protonation and xylose binding, and not glucose,
sets up the transporter for conformational switch. Overall, we
demonstrate the unique ability of HDX-MS to distinguish between
the conformational dynamics of inhibitor and substrate binding,
and show that a specific allosteric coupling between substrate
binding and protonation is a key step to initiate transport.
