Opposite movement of the external gate of a glutamate transporter homolog upon binding cotransported sodium compared with substrate

Paul J. Focke, Pierre Moenne-Loccoz, Hans P Larsson

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Recently, a new model for glutamate uptake by glutamate transporters was proposed based on crystal structures of the bacterial glutamate transporter homolog GltPh.It was proposed that hairpin two (HP2) functions as the extra cellular gate and that Na + and glutamate binding closes HP2, thereby allowing for the translocation of the glutamate binding pocket across the membrane. However, the conformation of HP2 in the apo state and the Na + bound state is unknown. We here use double site-directed spin-labeling electron paramagnetic resonance spectroscopy on the bacterial transporter GltPh from Pyrococcus horikoshi to examine conformational changes in HP2. Surprisingly, the cotransported substrates Na + and as partate induce opposite movements of HP2. We find that in the apo state, HP2 is in a similar conformation as in the as partate-bound closed state. Na + binding to the apo state opens HP2, whereas the subsequent binding of as partate closes HP2. Our findings show that Na + binding opens and stabilizes the extra cellular gate, thereby allowing for amino acid substrate binding. In contrast, in the absence of Na + and as partate, HP2 closes, suggesting a potential mechanism for the translocation of the empty binding pocket necessary to complete the transport cycle. The finding that physiological Na + concentrations stabilize the open HP2 state would ensure that the outward-facing conformation of the transporter is maintained in physiological solutions and that glutamate transporters are ready to quickly bind glutamate released from glutamatergic synapses.

Original languageEnglish
Pages (from-to)6255-6262
Number of pages8
JournalJournal of Neuroscience
Volume31
Issue number16
DOIs
StatePublished - Apr 20 2011

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Amino Acid Transport System X-AG
Glutamic Acid
Sodium
Pyrococcus
Bacterial Structures
Electron Spin Resonance Spectroscopy
Synapses
Spectrum Analysis
Amino Acids
Membranes

ASJC Scopus subject areas

  • Neuroscience(all)

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Opposite movement of the external gate of a glutamate transporter homolog upon binding cotransported sodium compared with substrate. / Focke, Paul J.; Moenne-Loccoz, Pierre; Larsson, Hans P.

In: Journal of Neuroscience, Vol. 31, No. 16, 20.04.2011, p. 6255-6262.

Research output: Contribution to journalArticle

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