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bioRxiv · 10.1101/555565

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

LeVine, M. V.·Terry, D. S.·Khelashvili, G.·Siegel, Z. S.·Quick, M.·Javitch, J. A.·Blanchard, S. C.·Weinstein, H.
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Abstract

Neurotransmitter:sodium symporters (NSS) 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. While a combination of structural, functional, and computational studies on LeuT, a bacterial NSS homolog, has provided critical insight into the mechanism of sodium-coupled transport, the mechanism underlying substrate-specific transport rates is still not understood. We present a combination of MD simulations, single-molecule FRET imaging, and measurements of Na+ binding and substrate transport that reveal an allosteric mechanism in which residues F259 and I359 in the substrate binding pocket couple substrate binding to Na+ release from the Na2 site through allosteric modulation of the stability of a partially-open, inward-facing state. We propose a new model for transport selectivity in which the two residues act as a volumetric sensor that inhibits the transport of bulky amino acids.

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LeVine, M. V., Terry, D. S., Khelashvili, G., Siegel, Z. S., Quick, M., Javitch, J. A., Blanchard, S. C., Weinstein, H.. 2019-02-20. The allosteric mechanism of substrate-specific transport in SLC6 is mediated by a volumetric sensor. https://doi.org/10.1101/555565

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