Jump to main content
Jump to site search

Issue 3, 2011
Previous Article Next Article

The mechanism of substrate release by the aspartate transporter GltPh: insights from simulations

Author affiliations

Abstract

Glutamate transporters regulate excitatory amino acid neurotransmission across neuronal and glial cell membranes by coupling the translocation of their substrate (aspartate or glutamate) into the intracellular (IC) medium to the energetically favorable transport of sodium ions or other cations. The first crystallographically resolved structure of this family, the archaeal aspartate transporter, GltPh, has served as a structural paradigm for elucidating the mechanism of substrate translocation by these transporters. Two helical hairpins, HP2 and HP1, at the core domains of the three subunits that form this membrane protein have been proposed to act as the respective extracellular and IC gates for substrate intake and release. Molecular dynamics simulations using the outward-facing structure have confirmed that the HP2 loop acts as an EC gate. The mechanism of substrate release at atomic scale, however, remained unknown due to the lack of structural data until the recent determination of the inward-facing structure of GltPh. In the present study, we use this recently resolved structure to simulate the release of substrate to the cytoplasm and the roles of HP1 and HP2 in this process. The highly flexible HP2 loop is observed to serve as an activator (or initiator) prompting the release of a gatekeeper Na+ to the cytoplasm and promoting the influx of water molecules from the cytoplasm, which effectively disrupt substrate–protein interactions and drive the dislodging of the substrate from its binding site. The completion of substrate release and exit, however, entails the opening of the highly stable HP1 loop as well. Overall, the unique conformational flexibility of the HP2 loop, the dissociation of a Na+, the hydration of binding pocket, and final yielding of the HP1 loop 3-Ser motif emerge as the successive events controlling the release of the bound substrate to the cell interior by glutamate transporters.

Graphical abstract: The mechanism of substrate release by the aspartate transporter GltPh: insights from simulations

Back to tab navigation

Supplementary files

Additions and corrections

Publication details

The article was received on 24 Aug 2010, accepted on 12 Nov 2010 and first published on 15 Dec 2010


Article type: Paper
DOI: 10.1039/C0MB00175A
Citation: Mol. BioSyst., 2011,7, 832-842
  •   Request permissions

    The mechanism of substrate release by the aspartate transporter GltPh: insights from simulations

    J. DeChancie, I. H. Shrivastava and I. Bahar, Mol. BioSyst., 2011, 7, 832
    DOI: 10.1039/C0MB00175A

Search articles by author

Spotlight

Advertisements