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Nat Struct Mol Biol. 2013 Feb;20(2):210-4. doi: 10.1038/nsmb.2471. Epub 2013 Jan 20.

Conformational heterogeneity of the aspartate transporter Glt(Ph).

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Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.


Glt(Ph) is a Pyrococcus horikoshii homotrimeric Na(+)-coupled aspartate transporter that belongs to the glutamate transporter family. Each protomer consists of a trimerization domain involved in subunit interaction and a transporting domain with the substrate-binding site. Here, we have studied the conformational changes underlying transport by Glt(Ph) using EPR spectroscopy. The trimerization domains form a rigid scaffold, whereas the transporting domains sample multiple conformations, consistent with large-scale movements during the transport cycle. Binding of substrates changed the occupancies of the different conformational states, but the domains remained heterogeneous. The membrane environment favored conformations different from those observed in detergent micelles, but the transporting domain remained structurally heterogeneous in both environments. We conclude that the transporting domains sample multiple conformational states with substantial occupancy regardless of the presence of substrate and coupling ions, consistent with equilibrium constants close to unity between the observed transporter conformations.

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