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Nat Struct Mol Biol. 2014 May;21(5):472-9. doi: 10.1038/nsmb.2816. Epub 2014 Apr 20.

Conformational dynamics of ligand-dependent alternating access in LeuT.

Author information

  • 11] Chemical and Physical Biology Program, Vanderbilt University, Nashville, Tennessee, USA. [2].
  • 21] Department of Molecular Physiology and Biophysics, Nashville, Tennessee, USA. [2].
  • 31] Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York, USA. [2] Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York, USA. [3] New York State Psychiatric Institute, Division of Molecular Therapeutics, New York, New York, USA.
  • 4Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.
  • 51] Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York, USA. [2] HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Medical College of Cornell University, New York, New York, USA.
  • 61] Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York, USA. [2] Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York, USA. [3] New York State Psychiatric Institute, Division of Molecular Therapeutics, New York, New York, USA. [4] Department of Pharmacology, Columbia University College of Physicians and Surgeons, New York, New York, USA.
  • 71] Chemical and Physical Biology Program, Vanderbilt University, Nashville, Tennessee, USA. [2] Department of Molecular Physiology and Biophysics, Nashville, Tennessee, USA.

Abstract

The leucine transporter (LeuT) from Aquifex aeolicus is a bacterial homolog of neurotransmitter/sodium symporters (NSSs) that catalyze reuptake of neurotransmitters at the synapse. Crystal structures of wild-type and mutants of LeuT have been interpreted as conformational states in the coupled transport cycle. However, the mechanistic identities inferred from these structures have not been validated, and the ligand-dependent conformational equilibrium of LeuT has not been defined. Here, we used distance measurements between spin-label pairs to elucidate Na(+)- and leucine-dependent conformational changes on the intracellular and extracellular sides of the transporter. The results identify structural motifs that underlie the isomerization of LeuT between outward-facing, inward-facing and occluded states. The conformational changes reported here present a dynamic picture of the alternating-access mechanism of LeuT and NSSs that is different from the inferences reached from currently available structural models.

PMID:
24747939
PMCID:
PMC4050370
DOI:
10.1038/nsmb.2816
[PubMed - indexed for MEDLINE]
Free PMC Article
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