Conformational Ensembles from Experimental Data and Computer Simulations

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Conformational Ensembles from Experimental Data
and Computer Simulations Tuesday Speaker Abstracts
30
Computation of Structural Ensembles from NMR and Other Data
Charles Schwieters
NIH, Bethesda, MD, USA
No Abstract
Mechanism of Substrate Translocation in an Alternating Access Transporter
Naomi Latorraca 1,2,3 , Nathan Fastman2,3 , Ron Dror1,2,3 , Liang Feng2,3.
1Stanford University, Stanford, CA, USA, 2Stanford University, Stanford, CA, USA, 3 Stanford
University, Stanford, CA, USA.
Transporters shuttle molecules across cell membranes by alternating among distinct
conformational states. Fundamental questions remain about how transporters transition between
states and how such structural rearrangements regulate substrate translocation. We captured the
translocation process by crystallography and unguided molecular dynamics simulations,
providing an atomic-level description of alternating access transport (Latorraca et al, Cell 2017).
Simulations of a SWEET-family transporter initiated from an outward-open, glucose-bound
structure reported here spontaneously adopt occluded and inward-open conformations.
Strikingly, these conformations match crystal structures, including our inward-open structure.
Mutagenesis experiments further validate simulation predictions. Our results reveal that state
transitions are driven by favorable interactions formed upon closure of extracellular and
intracellular “gates” and by an unfavorable transmembrane helix configuration when both gates
are closed. This mechanism leads to tight allosteric coupling between gates, preventing them
from opening simultaneously. Interestingly, the substrate appears to take a “free ride” across the
membrane without causing major structural rearrangements in the transporter.