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Sci Adv. 2018 May 11;4(5):eaar6179. doi: 10.1126/sciadv.aar6179. eCollection 2018 May.

Substrate-modulated unwinding of transmembrane helices in the NSS transporter LeuT.

Author information

1
Protein Analysis Group, Department of Pharmacy, University of Copenhagen, 2100 Copenhagen O, Denmark.
2
Department of Neuroscience, University of Copenhagen, 2200 Copenhagen N, Denmark.
3
Molecular Modeling Group, Swiss Institute of Bioinformatics, Lausanne, Switzerland.

Abstract

LeuT, a prokaryotic member of the neurotransmitter:sodium symporter (NSS) family, is an established structural model for mammalian NSS counterparts. We investigate the substrate translocation mechanism of LeuT by measuring the solution-phase structural dynamics of the transporter in distinct functional states by hydrogen/deuterium exchange mass spectrometry (HDX-MS). Our HDX-MS data pinpoint LeuT segments involved in substrate transport and reveal for the first time a comprehensive and detailed view of the dynamics associated with transition of the transporter between outward- and inward-facing configurations in a Na+- and K+-dependent manner. The results suggest that partial unwinding of transmembrane helices 1/5/6/7 drives LeuT from a substrate-bound, outward-facing occluded conformation toward an inward-facing open state. These hitherto unknown, large-scale conformational changes in functionally important transmembrane segments, observed for LeuT in detergent-solubilized form and when embedded in a native-like phospholipid bilayer, could be of physiological relevance for the translocation process.

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