Mechanism of Substrate Translocation in an Alternating Access Transporter

Latorraca, Naomi R.; Fastman, Nathan M.; Venkatakrishnan, AJ; Frommer, Wolf B.; Dror, Ron O.; Feng, Liang

doi:10.1016/j.cell.2017.03.010

Cited by 95 publications

(128 citation statements)

References 76 publications

(90 reference statements)

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“…SWEETs are a class of seven transmembrane hexose and sucrose uniporters that function as oligomers (Chen et al, 2010;Xuan et al, 2013). It has been proposed that AtSWEET13 functions as a 'revolving door' mechanism to accelerate the transport efficacy (Feng & Frommer, 2015;Han et al, 2017;Latorraca et al, 2017). Roles of SWEETs include phloem loading and nectar secretion, and they have been shown to act as susceptibility factors for pathogen infections (Chen et al, 2010(Chen et al, , 2012Lin et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

SWEET11 and 15 as key players in seed filling in rice

et al. 2018

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SummaryDespite the relevance of seed-filling mechanisms for crop yield, we still have only a rudimentary understanding of the transport processes that supply the caryopsis with sugars. We hypothesized that SWEET sucrose transporters may play important roles in nutrient import pathways in the rice caryopsis.We used a combination of mRNA quantification, histochemical analyses, translational promoter-reporter fusions and analysis of knockout mutants created by genomic editing to evaluate the contribution of SWEET transporters to seed filling.In rice caryopses, SWEET11 and 15 had the highest mRNA levels and proteins localized to four key sites: all regions of the nucellus at early stages; the nucellar projection close to the dorsal vein; the nucellar epidermis that surrounds the endosperm; and the aleurone. ossweet11;15 double knockout lines accumulated starch in the pericarp, whereas caryopses did not contain a functional endosperm.Jointly, SWEET11 and 15 show all the hallmarks of being necessary for seed filling with sucrose efflux functions at the nucellar projection and a role in transfer across the nucellar epidermis/aleurone interface, delineating two major steps for apoplasmic seed filling, observations that are discussed in relation to observations made in rice and barley regarding the relative prevalence of these two potential import routes.

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Section: Introductionmentioning

confidence: 99%

SWEET11 and 15 as key players in seed filling in rice

et al. 2018

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“…SWEETs are a class of transporters with seven transmembrane helices that function as hexose or sucrose uniporters (Xuan et al, 2013). Multiple SemiSWEETs and SWEETs have been crystallized, and AtSWEET13 has been proposed to function in complexes via a 'revolving door' mechanism to accelerate transport efficacy (Feng & Frommer, 2015;Han et al, 2017;Latorraca et al, 2017). In Arabidopsis, SWEET roles include phloem loading, nectar secretion, pollen nutrition and seed filling Sun et al, 2013;Lin et al, 2014;Sosso et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Impaired phloem loading in zmsweet13a,b,c sucrose transporter triple knock‐out mutants in Zea mays

et al. 2018

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SummaryCrop yield depends on efficient allocation of sucrose from leaves to seeds. In Arabidopsis, phloem loading is mediated by a combination of SWEET sucrose effluxers and subsequent uptake by SUT1/SUC2 sucrose/H + symporters. ZmSUT1 is essential for carbon allocation in maize, but the relative contribution to apoplasmic phloem loading and retrieval of sucrose leaking from the translocation path is not known.Here we analysed the contribution of SWEETs to phloem loading in maize.We identified three leaf-expressed SWEET sucrose transporters as key components of apoplasmic phloem loading in Zea mays L. ZmSWEET13 paralogues (a, b, c) are among the most highly expressed genes in the leaf vasculature. Genome-edited triple knock-out mutants were severely stunted. Photosynthesis of mutants was impaired and leaves accumulated high levels of soluble sugars and starch. RNA-seq revealed profound transcriptional deregulation of genes associated with photosynthesis and carbohydrate metabolism. Genome-wide association study (GWAS) analyses may indicate that variability in ZmSWEET13s correlates with agronomical traits, especifically flowering time and leaf angle.This work provides support for cooperation of three ZmSWEET13s with ZmSUT1 in phloem loading in Z. mays.

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“…12 Crystal structures of SemiSWEETs in different conformational states (i.e. inward-open (IF), 10,13 occluded (OC) 9 and outward-open (OF) 10,13 state) have provided the opportunity to understand the functional mechanisms of these proteins in atomistic detail. The distinct conformations of SemiSWEETs highlight that its transport mechanism is based on the principle of alternate-access.…”

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confidence: 99%

“…Recent molecular simulation study of LbSemiSWEET proposed a "free-ride" mechanism of glucose transport, where the term "free-ride" was used to imply that glucose diffuses freely from the extracellular to intracellular side without inducing major conformational changes in the transporter. 13 From a structural viewpoint, there are no major helical shifts while glucose is being transported. It is not clear if similar mechanism applies to the SWEET transporters as well.…”

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Molecular Basis of Glucose Transport Mechanism in Plants

Selvam¹,

Yu²,

Chen³

et al. 2019

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<p>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. 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 OsSWEET2b transporter using extensive molecular dynamics simulations. Using Markov state models, we estimated the free energy barrier associated with different states as well as 1 for the glucose the transport mechanism. SWEETs undergoes structural transition to outward-facing (OF), Occluded (OC) and inward-facing (IF) and strongly support 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 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 act 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.</p>

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Mechanism of Substrate Translocation in an Alternating Access Transporter

Cited by 95 publications

References 76 publications

SWEET11 and 15 as key players in seed filling in rice

SWEET11 and 15 as key players in seed filling in rice

Impaired phloem loading in zmsweet13a,b,c sucrose transporter triple knock‐out mutants in Zea mays

Molecular Basis of Glucose Transport Mechanism in Plants

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