Molecular Basis of the Glucose Transport Mechanism
in Plants
Version 5 2019-06-26, 07:29
Version 4 2019-05-30, 14:12
Version 3 2019-05-30, 14:09
Version 2 2019-05-29, 17:45
Version 1 2019-05-29, 17:40
Posted on 2019-06-26 - 07:29
The SWEET family belongs to a class of transporters in plants that
undergoes large conformational changes to facilitate transport of
sugar molecules across the cell membrane (SWEET, Sugars Will Eventually
Be Exported Transporter). However, the structures of their functionally
relevant conformational states in the transport cycle have not been
reported. In this study, we have characterized the conformational
dynamics and complete transport cycle of glucose in the OsSWEET2b
transporter using extensive molecular dynamics simulations. Using
Markov state models, we estimated the free energy barrier associated
with different states as well as for the glucose transport mechanism.
SWEETs undergo a structural transition to outward-facing (OF), occluded
(OC), and inward-facing (IF) and strongly support an alternate access
transport mechanism. The glucose diffuses freely from outside to inside
the cell without causing major conformational changes which means
that the conformations of glucose unbound and bound snapshots are
exactly the same for OF, OC, and IF states. We identified a network
of hydrophobic core residues at the center of the transporter that
restricts the glucose entry to the cytoplasmic side and acts as an
intracellular hydrophobic gate. The mechanistic predictions from molecular
dynamics simulations are validated using site-directed mutagenesis
experiments. Our simulation also revealed hourglass-like intermediate
states making the pore radius narrower at the center. This work provides
new fundamental insights into how substrate–transporter interactions
actively change the free energy landscape of the transport cycle to
facilitate enhanced transport activity.
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Selvam, Balaji; Yu, Ya-Chi; Chen, Li-Qing; Shukla, Diwakar (2019). Molecular Basis of the Glucose Transport Mechanism
in Plants. ACS Publications. Collection. https://doi.org/10.1021/acscentsci.9b00252
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AUTHORS (4)
BS
Balaji Selvam
YY
Ya-Chi Yu
LC
Li-Qing Chen
DS
Diwakar Shukla