SWEET transporters

Last updated
SemiSWEET PQ-loop
Identifiers
SymbolPQ-loop
Pfam PF03083
Pfam clan PQ-loop
InterPro IPR006603
SMART SM00679
TCDB 2.A.123
OPM superfamily 415
OPM protein 5ctg
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary

The SWEET family (Sugars Will Eventually Be Exported Transporter), also known as the PQ-loop, Saliva or MtN3 family (TC# 2.A.123), is a family of sugar transporters and a member of the TOG superfamily. The proteins of the SWEET family have been found in plants, animals, protozoans, and bacteria. Eukaryotic family members have 7 transmembrane segments (TMSs) in a 3+1+3 repeat arrangement. [1]

Contents

Function

Proteins of the SWEET family appear to catalyze facilitated diffusion (entry or export) of sugars across the plant plasma membrane or the endoplasmic reticulum membrane. [2]

They also seem to transport other metabolites, like gibberellins. [3]

Transport Reaction

The generalized reaction catalyzed by known proteins of this family is: [1]

sugars (in) ⇌ sugars (out)

Discovery

SWEETs were originally identified in Arabidopsis thaliana, in a screen for novel facilitators of transmembrane glucose transport. In this experiment, several previously uncharacterized membrane proteins were selected to be screened. These uncharacterized membrane proteins were assayed for glucose transport ability by expression in HEK293T (human embryonic kidney) cells, which have negligible glucose transport ability in the normal state. These membrane proteins were co-expressed with a fluorescent FRET (Förster resonance energy transfer) glucose sensor localized to the endoplasmic reticulum (ER). [4] [5] [6] [7] [8] [9] Glucose movement from the cytoplasm to the ER of the HEK293T cells was monitored by quantifying changes in FRET ratio. By using this assay, the first member of the SWEET family, AtSWEET1, was identified. Other potential family members were identified by sequence homology. [10]

Homologues

Chen et al. (2010) reviewed evidence for a new class of sugar transporters, named SWEETs. [10] Those that mediate glucose transport include at least six out of seventeen sugar homologues in Arabidopsis (i.e., TC#s 2.A.123.1.3, 2.A.123.1.5, 2.A.123.1.9, 2.A.123.1.13), two out of over twenty porters in rice (TC#s 2.A.123.1.6 and 2.A.123.1.18), two out of seven homologues in Caenorhabditis elegans (i.e., TC# 2.A.123.1.10) and the single copy human protein (SLC50A1 of Homo sapiens, TC# 2.A.123.1.4). Without Arabidopsis SWEET8 (TC# 2.A.123.1.5), pollen is not viable. The corn homolog ZmSWEET4c was shown to be involved in seed filling. [11]

Currently classified members of the SWEET transporter family can be found in the Transporter Classification Database.

SWEETs in plants

Plant SWEETs fall into four subclades. [10] The tomato genome encodes 29 SWEETs. [12]

SWEET9 in Nectar Secretion

Lin et al., 2014, examined the role of SWEET9 in nectaries. SWEET9 is a member of clade 3. A homologue in petunias had been shown to have an inverse correlation between expression and starch content in nectaries. Mutation and overexpression of SWEET9 in Arabidopsis led to corresponding loss of and increase in nectar secretion, respectively. After showing that SWEET9 is involved in nectar secretion, the next step was to determine at which phase of the process SWEET9 has its function. The 3 options were: phloem unloading, or uptake or efflux from nectary parenchyma. A combination of localization studies and starch accumulation assays showed that SWEET9 is involved in sucrose efflux from the nectary parenchyma. [13]

SWEETs 11, 12, and 15 in Embryo Nutrition

Chen et al., 2015, asked what SWEETs are involved in providing nutrition to an embryo. The team noticed that mRNA and protein for SWEETs 11, 12, and 15 are each expressed at high levels during some stage of embryo development. Each gene was subsequently mutated to generate a sweet11;12;15 triple mutant which lacked activity in each of the three genes. This triple mutant was shown to have delayed embryo development; that is, the seeds of the triple mutant were significantly smaller than that of the wild type at the same time during development. The starch content of the seed coat was higher than the wild-type, and the starch content of the embryo was lower than the wild-type. Additionally, protein levels were shown to be maternally controlled: in a sweet11;12;15 mutant crossed with a wild-type plant, the mutant phenotype was only seen when sweet11;12;15 was used as the maternal plant. [14]

Structure

3.1 A resolution structure of a eukaryotic SWEET transporter in a homotrimer (5CTG, OsSWEET2). Each different color represents one subunit. 3.1 A resolution structure of a eukaryotic SWEET transporter.png
3.1 A resolution structure of a eukaryotic SWEET transporter in a homotrimer (5CTG, OsSWEET2). Each different color represents one subunit.

Many bacterial homologues have only 3 TMSs and are half sized, but they nevertheless are members of the SWEET family with a single 3 TMS repeat unit. Other bacterial homologues have 7 TMSs as do most eukaryotic proteins in this family. The SWEET family is large and diverse. Based on 3-D structural analyses, it is likely that these paired 3 TMS SWEET family members function as carriers.

Bacterial SemiSWEETs, consist of a triple-helix bundle in a 1-3-2 conformation, with TM3 sandwiched between TM1 and TM2. [15] The structures also show tryptophan and asparagine residues interacting with the sugar; point mutations of these residues to alanine destroys the hexose transport function of SemiSWEET. [15] The SWEET family is a member of the TOG superfamily which is believed to have arisen via the pathway:

2 TMSs --> 4 TMSs --> 8 TMSs --> 7 TMSs --> 3 + 3 TMSs. [16]

Several crystal structures are available on RCSB for members of the SWEET/SemiSWEET/PQ-loop/Saliva/MtN3 family.

See also

Related Research Articles

<span class="mw-page-title-main">GLUT2</span> Transmembrane carrier protein

Glucose transporter 2 (GLUT2) also known as solute carrier family 2, member 2 (SLC2A2) is a transmembrane carrier protein that enables protein facilitated glucose movement across cell membranes. It is the principal transporter for transfer of glucose between liver and blood Unlike GLUT4, it does not rely on insulin for facilitated diffusion.

Glucose transporter 3, also known as solute carrier family 2, facilitated glucose transporter member 3 (SLC2A3) is a protein that in humans is encoded by the SLC2A3 gene. GLUT3 facilitates the transport of glucose across the plasma membranes of mammalian cells. GLUT3 is most known for its specific expression in neurons and has originally been designated as the neuronal GLUT. GLUT3 has been studied in other cell types with specific glucose requirements, including sperm, preimplantation embryos, circulating white blood cells and carcinoma cell lines.

<span class="mw-page-title-main">SLC2A9</span> Protein-coding gene in the species Homo sapiens

Solute carrier family 2, facilitated glucose transporter member 9 is a protein that in humans is encoded by the SLC2A9 gene.

<span class="mw-page-title-main">Turanose</span> Chemical compound

Turanose is a reducing disaccharide. The d-isomer is naturally occurring. Its systematic name is α-d-glucopyranosyl-(1→3)-α-d-fructofuranose. It is an analog of sucrose not metabolized by higher plants, but rather acquired through the action of sucrose transporters for intracellular carbohydrate signaling. In addition to its involvement in signal transduction, d-(+)-turanose can also be used as a carbon source by many organisms including numerous species of bacteria and fungi.

<span class="mw-page-title-main">Sodium-solute symporter</span> Group of transport proteins

Members of the Solute:Sodium Symporter (SSS) Family (TC# 2.A.21) catalyze solute:Na+ symport. The SSS family is within the APC Superfamily. The solutes transported may be sugars, amino acids, organo cations such as choline, nucleosides, inositols, vitamins, urea or anions, depending on the system. Members of the SSS family have been identified in bacteria, archaea and eukaryotes. Almost all functionally well-characterized members normally catalyze solute uptake via Na+ symport.

Stp4 is a gene from the model plant, Arabidopsis thaliana. The gene transcribes for an integral membrane protein that is situated in the plasma membrane of sink tissues such as roots, anthers and vascular tissue.

<span class="mw-page-title-main">Sugar transporter SWEET1</span> Protein-coding gene in the species Homo sapiens

Sugar transporter SWEET1, also known as RAG1-activating protein 1 and stromal cell protein (SCP), is a membrane protein that in humans is encoded by the SLC50A1 gene. SWEET1 is the sole transporter from the SLC50 (SWEET) gene family present in the genomes of most animal species, with the exception of the nematode Caenorhabditis elegans, which has seven.

The transporter-opsin-G protein-coupled receptor (TOG) superfamily is a protein superfamily of integral membrane proteins, usually of 7 or 8 transmembrane alpha-helical segments (TMSs). It includes (1) ion-translocating microbial rhodopsins and (2) G protein-coupled receptors (GPCRs), (3) Sweet sugar transporters, (4) nicotinamide ribonucleoside uptake permeases (PnuC; TC# 4.B.1), (5) 4-toluene sulfonate uptake permeases (TSUP); TC# 2.A.102), (6) Ni2+–Co2+ transporters (NiCoT); TC# 2.A.52), (7) organic solute transporters (OST); TC# 2.A.82), (8) phosphate:Na+ symporters (PNaS); TC# 2.A.58) and (9) lysosomal cystine transporters (LCT); TC# 2.A.43).

The amino acid-polyamine-organocation (APC) superfamily is the second largest superfamily of secondary carrier proteins currently known, and it contains several Solute carriers. Originally, the APC superfamily consisted of subfamilies under the transporter classification number. This superfamily has since been expanded to include eighteen different families.

The anion exchanger family is a member of the large APC superfamily of secondary carriers. Members of the AE family are generally responsible for the transport of anions across cellular barriers, although their functions may vary. All of them exchange bicarbonate. Characterized protein members of the AE family are found in plants, animals, insects and yeast. Uncharacterized AE homologues may be present in bacteria. Animal AE proteins consist of homodimeric complexes of integral membrane proteins that vary in size from about 900 amino acyl residues to about 1250 residues. Their N-terminal hydrophilic domains may interact with cytoskeletal proteins and therefore play a cell structural role. Some of the currently characterized members of the AE family can be found in the Transporter Classification Database.

The sulfate permease (SulP) family is a member of the large APC superfamily of secondary carriers. The SulP family is a large and ubiquitous family of proteins derived from archaea, bacteria, fungi, plants and animals. Many organisms including Bacillus subtilis, Synechocystis sp, Saccharomyces cerevisiae, Arabidopsis thaliana and Caenorhabditis elegans possess multiple SulP family paralogues. Many of these proteins are functionally characterized, and most are inorganic anion uptake transporters or anion:anion exchange transporters. Some transport their substrate(s) with high affinities, while others transport it or them with relatively low affinities. Others may catalyze SO2−
4:HCO−
3 exchange, or more generally, anion:anion antiport. For example, the mouse homologue, SLC26A6, can transport sulfate, formate, oxalate, chloride and bicarbonate, exchanging any one of these anions for another. A cyanobacterial homologue can transport nitrate. Some members can function as channels. SLC26A3 and SLC26A6 can function as carriers or channels, depending on the transported anion. In these porters, mutating a glutamate, also involved in transport in the CIC family, created a channel out of the carrier. It also changed the stoichiometry from 2Cl−/HCO−
3 to 1Cl−/HCO−
3.

The potassium (K+) uptake permease (KUP) family (TC# 2.A.72) is a member of the APC superfamily of secondary carriers. Proteins of the KUP/HAK/KT family include the KUP (TrkD) protein of E. coli and homologues in both Gram-positive and Gram-negative bacteria. High affinity (20 μM) K+ uptake systems (Hak1, TC# 2.A.72.2.1) of the yeast Debaryomyces occidentalis as well as the fungus, Neurospora crassa, and several homologues in plants have been characterized. Arabidopsis thaliana and other plants possess multiple KUP family paralogues. While many plant proteins cluster tightly together, the Hak1 proteins from yeast as well as the two Gram-positive and Gram-negative bacterial proteins are distantly related on the phylogenetic tree for the KUP family. All currently classified members of the KUP family can be found in the Transporter Classification Database.

The Ca2+:cation antiporter (CaCA) family (TC# 2.A.19) is a member of the cation diffusion facilitator (CDF) superfamily. This family should not be confused with the Ca2+:H+ Antiporter-2 (CaCA2) Family (TC# 2.A.106) which belongs to the Lysine Exporter (LysE) Superfamily. Proteins of the CaCA family are found ubiquitously, having been identified in animals, plants, yeast, archaea and divergent bacteria. Members of this family facilitate the antiport of calcium ion with another cation.

The multidrug/oligosaccharidyl-lipid/polysaccharide (MOP) flippase superfamily is a group of integral membrane protein families. The MOP flippase superfamily includes twelve distantly related families, six for which functional data are available:

  1. One ubiquitous family (MATE) specific for drugs - (TC# 2.A.66.1) The Multi Antimicrobial Extrusion (MATE) Family
  2. One (PST) specific for polysaccharides and/or their lipid-linked precursors in prokaryotes - (TC# 2.A.66.2) The Polysaccharide Transport (PST) Family
  3. One (OLF) specific for lipid-linked oligosaccharide precursors of glycoproteins in eukaryotes - (TC# 2.A.66.3) The Oligosaccharidyl-lipid Flippase (OLF) Family
  4. One (MVF) lipid-peptidoglycan precursor flippase involved in cell wall biosynthesis - (TC# 2.A.66.4) The Mouse Virulence Factor (MVF) Family
  5. One (AgnG) which includes a single functionally characterized member that extrudes the antibiotic, Agrocin 84 - (TC# 2.A.66.5) The Agrocin 84 Antibiotic Exporter (AgnG) Family
  6. And finally, one (Ank) that shuttles inorganic pyrophosphate (PPi) - (TC# 2.A.66.9) The Progressive Ankylosis (Ank) Family

The Tellurium Ion Resistance (TerC) Family is part of the Lysine Exporter (LysE) Superfamily. A representative list of proteins belonging to the TerC family can be found in the Transporter Classification Database.

The Nickel/Cobalt Transporter (NicO) Family is a member of the Lysine Exporter (LysE) Superfamily.

The p-aminobenzoyl-glutamate transporter(AbgT) family (TC# 2.A.68) is a family of transporter proteins belonging to the ion transporter (IT) superfamily. The AbgT family consists of the AbgT (YdaH; TC# 2.A.68.1.1) protein of E. coli and the MtrF drug exporter (TC# 2.A.68.1.2) of Neisseria gonorrhoeae. The former protein is apparently cryptic in wild-type cells, but when expressed on a high copy number plasmid, or when expressed at higher levels due to mutation, it appeared to allow uptake (Km = 123 nM; see Michaelis–Menten kinetics) and subsequent utilization of p-aminobenzoyl-glutamate as a source of p-aminobenzoate for p-aminobenzoate auxotrophs. p-Aminobenzoate is a constituent of and a precursor for the biosynthesis of folic acid. MtrF was annotated as a putative drug efflux pump.

The Pho1 phosphate permease family is a family of phosphate transporters belonging to the ion transporter (IT) superfamily. Representative members of the Pho1 family include the putative phosphate transporter PHO1 of Arabidopsis thaliana, and the xenotropic and polytropic murine-leukemia virus receptor Xpr1 of Culex pipiens.

The 6TMS Neutral Amino Acid Transporter (NAAT) Family is a family of transporters belonging to the Lysine Exporter (LysE) Superfamily. Homologues are found in numerous Gram-negative and Gram-positive bacteria including many human pathogens. Several archaea also encode MarC homologues. Some of these organisms have 2 or more paralogues. Most of these proteins are of about the same size although a few are larger. They exhibit 6 putative TMSs. A representative list of members belonging to the NAAT family can be found in the Transporter Classification Database.

<span class="mw-page-title-main">Monovalent cation:proton antiporter-1</span> Family of proteins

The Monovalent Cation:Proton Antiporter-1 (CPA1) Family (TC# 2.A.36) is a large family of proteins derived from Gram-positive and Gram-negative bacteria, blue-green bacteria, archaea, yeast, plants and animals. The CPA1 family belongs to the VIC superfamily. Transporters from eukaryotes have been functionally characterized to catalyze Na+:H+ exchange. Their primary physiological functions are thought to be in (1) cytoplasmic pH regulation, extruding the H+ generated during metabolism, and (2) salt tolerance (in plants), due to Na+ uptake into vacuoles. Bacterial homologues have also been found to facilitate Na+:H+ antiport, but some also catalyze Li+:H+ antiport or Ca2+:H+ antiport under certain conditions.

References

  1. 1 2 Saier, MH Jr. "2.A.123 The Sweet; PQ-loop; Saliva; MtN3 (Sweet) Family". Transporter Classification Database. Saier Lab Bioinformatics Group / SDSC.
  2. ↑ Takanaga H, Frommer WB (August 2010). "Facilitative plasma membrane transporters function during ER transit". FASEB Journal. 24 (8): 2849–58. doi: 10.1096/fj.09-146472 . PMC   3230527 . PMID   20354141.
  3. ↑ Kanno Y, Oikawa T, Chiba Y, Ishimaru Y, Shimizu T, Sano N, Koshiba T, Kamiya Y, Ueda M, Seo M (October 2016). "AtSWEET13 and AtSWEET14 regulate gibberellin-mediated physiological processes". Nat Commun. 7 (13245): 13245. Bibcode:2016NatCo...713245K. doi:10.1038/ncomms13245. PMC   5095183 . PMID   27782132.
  4. ↑ "Nanosensors | Department of Plant Biology". dpb.carnegiescience.edu. Retrieved 1 March 2016.
  5. ↑ Bermejo C, Ewald JC, Lanquar V, Jones AM, Frommer WB (August 2011). "In vivo biochemistry: quantifying ion and metabolite levels in individual cells or cultures of yeast". The Biochemical Journal. 438 (1): 1–10. doi:10.1042/BJ20110428. PMID   21793803. S2CID   26944897.
  6. ↑ Jones AM, Grossmann G, Danielson JÅ, Sosso D, Chen LQ, Ho CH, Frommer WB (June 2013). "In vivo biochemistry: applications for small molecule biosensors in plant biology". Current Opinion in Plant Biology. 16 (3): 389–95. Bibcode:2013COPB...16..389J. doi:10.1016/j.pbi.2013.02.010. PMC   3679211 . PMID   23587939.
  7. ↑ Jones AM, Ehrhardt DW, Frommer WB (May 2012). "A never ending race for new and improved fluorescent proteins". BMC Biology. 10: 39. doi: 10.1186/1741-7007-10-39 . PMC   3342923 . PMID   22554191.
  8. ↑ Okumoto S, Jones A, Frommer WB (1 January 2012). "Quantitative imaging with fluorescent biosensors". Annual Review of Plant Biology. 63: 663–706. doi:10.1146/annurev-arplant-042110-103745. PMID   22404462.
  9. ↑ Hou BH, Takanaga H, Grossmann G, Chen LQ, Qu XQ, Jones AM, Lalonde S, Schweissgut O, Wiechert W, Frommer WB (October 2011). "Optical sensors for monitoring dynamic changes of intracellular metabolite levels in mammalian cells". Nature Protocols. 6 (11): 1818–33. doi:10.1038/nprot.2011.392. PMID   22036884. S2CID   21852318.
  10. 1 2 3 Chen LQ, Hou BH, Lalonde S, Takanaga H, Hartung ML, Qu XQ, Guo WJ, Kim JG, Underwood W, Chaudhuri B, Chermak D, Antony G, White FF, Somerville SC, Mudgett MB, Frommer WB (November 2010). "Sugar transporters for intercellular exchange and nutrition of pathogens". Nature. 468 (7323): 527–32. Bibcode:2010Natur.468..527C. doi:10.1038/nature09606. PMC   3000469 . PMID   21107422.
  11. ↑ Sosso D, Luo D, Li QB, Sasse J, Yang J, Gendrot G, Suzuki M, Koch KE, McCarty DR, Chourey PS, Rogowsky PM, Ross-Ibarra J, Yang B, Frommer WB (December 2015). "Seed filling in domesticated maize and rice depends on SWEET-mediated hexose transport". Nature Genetics. 47 (12): 1489–93. doi:10.1038/ng.3422. PMID   26523777. S2CID   6985808.
  12. ↑ Feng CY, Han JX, Han XX, Jiang J (December 2015). "Genome-wide identification, phylogeny, and expression analysis of the SWEET gene family in tomato". Gene. 573 (2): 261–72. doi:10.1016/j.gene.2015.07.055. PMID   26190159.
  13. ↑ Lin IW, Sosso D, Chen LQ, Gase K, Kim SG, Kessler D, Klinkenberg PM, Gorder MK, Hou BH, Qu XQ, Carter CJ, Baldwin IT, Frommer WB (April 2014). "Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9". Nature. 508 (7497): 546–9. Bibcode:2014Natur.508..546L. doi:10.1038/nature13082. PMID   24670640. S2CID   4384123.
  14. ↑ Chen LQ, Lin IW, Qu XQ, Sosso D, McFarlane HE, Londoño A, Samuels AL, Frommer WB (March 2015). "A cascade of sequentially expressed sucrose transporters in the seed coat and endosperm provides nutrition for the Arabidopsis embryo". The Plant Cell. 27 (3): 607–19. doi:10.1105/tpc.114.134585. PMC   4558658 . PMID   25794936.
  15. 1 2 Xu Y, Tao Y, Cheung LS, Fan C, Chen LQ, Xu S, Perry K, Frommer WB, Feng L (November 2014). "Structures of bacterial homologues of SWEET transporters in two distinct conformations". Nature. 515 (7527): 448–452. Bibcode:2014Natur.515..448X. doi:10.1038/nature13670. PMC   4300204 . PMID   25186729.
  16. ↑ Yee DC, Shlykov MA, Västermark A, Reddy VS, Arora S, Sun EI, Saier MH (November 2013). "The transporter-opsin-G protein-coupled receptor (TOG) superfamily". The FEBS Journal. 280 (22): 5780–800. doi:10.1111/febs.12499. PMC   3832197 . PMID   23981446.

Further reading

As of 2 February 2016, this article is derived in whole or in part from Transporter Classification Database . The copyright holder has licensed the content in a manner that permits reuse under CC BY-SA 3.0 and GFDL. All relevant terms must be followed.The original text was at "2.A.123 The Sweet; PQ-loop; Saliva; MtN3 (Sweet) Family"

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.