Interplay between phosphorylation and oligomerization tunes the conformational ensemble of SWEET transporters

Abstract

SWEET sugar transporters are desirable biotechnological targets for improving plant growth. One engineering strategy includes modulating how SWEET transporters are regulated. Phosphorylation and oligomerization have been shown to positively regulate SWEET function, leading to increased sugar transport activity. However, constitutive phosphorylation may not be beneficial to plant health under basal conditions. Structural and mechanistic understanding of the interplay between phosphorylation and oligomerization in functional regulation of SWEETs remains limited. Using extensive molecular dynamics simulations coupled with Markov state models, we demonstrate the thermodynamic and kinetic effects of SWEET phosphorylation and oligomerization using OsSWEET2b as a model. We report that the beneficial effects of these SWEET regulatory mechanisms bias outward-facing states and improved extracellular gating, which complement published experimental findings. Our results offer molecular insights to SWEET regulation and may guide engineering strategies throughout the SWEET transport family.

SWEET family transporters act as water conducting carrier proteins in plants

“…[54][55][56][57][58][59][60] In particular, SWEET family transporters form hetero-and homo-oligomers and have conserved phosphorylation sites that regulate substrate transport. 22,53,61 It is not clear how these regulatory mechanisms could impact the water transport function of the SWEETs. Therefore, further simulation studies are needed to establish the impact of phosphorylation and oligomerization on the water transport activity of SWEETs.…”

“…Sugar transporters play an important role in translocating sugars across different cells or different cellular compartments. In our previous studies, the functionally important intermediate states of SWEET [20][21][22][23] and SemiSWEET 24,25 transporters as well as the complete cycle of sugar transport has been characterized using large-scale Molecular Dynamics (MD) simulations and Markov State Modeling of the transporter dynamics. Markov state modeling of membrane transporters quantifies the thermodynamics and kinetics associated with the transports process and aids in the investigation of structure-function relationship of the complex membrane proteins.…”