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Title: The allosteric mechanism of substrate-specific transport in SLC6 is mediated by a volumetric sensor

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America

Neurotransmitter:sodium symporters (NSSs) in the SLC6 family terminate neurotransmission by coupling the thermodynamically favorable transport of ions to the thermodynamically unfavorable transport of neurotransmitter back into presynaptic neurons. Results from many structural, functional, and computational studies on LeuT, a bacterial NSS homolog, have provided critical insight into the mechanism of sodium-coupled transport, but the mechanism underlying substrate-specific transport rates is still not understood. We present a combination of molecular dynamics simulations, single-molecule fluorescence resonance energy transfer (smFRET) imaging, and measurements of Na+ binding and substrate transport that reveals an allosteric substrate specificity mechanism. In this mechanism, residues F259 and I359 in the substrate binding pocket couple the binding of substrate to Na+ release from the Na2 site by allosterically modulating the stability of a partially open, inward-facing state. We propose a model for transport selectivity in which residues F259 and I359 act as a volumetric sensor that inhibits the transport of bulky amino acids.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC) (OLCF); Univ. of California, Oakland, CA (United States); UT-Battelle LLC/ORNL, Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR); National Institutes of Health (NIH); National Science Foundation (NSF)
Grant/Contract Number:
AC02-05CH11231; AC05-00OR22725; R21-MH099491; U54-GM087510; P01-DA012408; R01-DA041510; F31-DA035533; ACI-1053575; R01-GM116961
OSTI ID:
1565765
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Vol. 116, Issue 32; ISSN 0027-8424
Publisher:
National Academy of SciencesCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 16 works
Citation information provided by
Web of Science

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Cited By (4)

The Amino Terminus of LeuT Changes Conformation in an Environment Sensitive Manner journal December 2019
Transmembrane helix 6b links proton and metal release pathways and drives conformational change in an Nramp-family transition metal transporter journal December 2019
Transmembrane helix 6b links proton and metal release pathways and drives conformational change in an Nramp-family transition metal transporter journal January 2020
X-ray structure of LeuT in an inward-facing occluded conformation reveals mechanism of substrate release journal February 2020