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{{Sandbox_Reserved_ESBS_2015}}
{{Sandbox_Reserved_ESBS_2015}}
==Structure and Functional aspects of Sucrose Synthase 1 from ''Arabidopsis thaliana''==
==Structure and Functional aspects of Sucrose Synthase 1 from ''Arabidopsis thaliana''==
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Sucrose Synthase 1 (EC:2.4.1.13), also known as the Sucrose-UDP glucolsyltransferase 1, is a reversible enzyme allowing the synthesis or the degradation of Sucrose in ''Arabidopsis thaliana''. It is a 360 kDa tetramer and belongs to the Glycosyltransferase subfamily 4 (GT4).
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Sucrose Synthase 1 (EC:2.4.1.13), also known as the sucrose-UDP glucolsyltransferase 1, is a reversible enzyme allowing the synthesis or the degradation of sucrose in ''Arabidopsis thaliana''. It is a 360 kDa tetramer and belongs to the Glycosyltransferase subfamily 4 (GT4).
<StructureSection scene='71/719877/Susy/7' size='340' side='right' caption='X-ray crystal structures of AtSus1, as a complex with UDP-glucose at 2.8-Å resolution and as a complex with UDP and fructose at 2.85-Å resolution'>
<StructureSection scene='71/719877/Susy/7' size='340' side='right' caption='X-ray crystal structures of AtSus1, as a complex with UDP-glucose at 2.8-Å resolution and as a complex with UDP and fructose at 2.85-Å resolution'>
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This reaction is a nucleophilic substitution involving a glycosyl intermediate. The glucose is transfered between UDP (donor) and fructose (acceptor).
This reaction is a nucleophilic substitution involving a glycosyl intermediate. The glucose is transfered between UDP (donor) and fructose (acceptor).
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This enzyme has a fundamental role in the Sucrose flow regulation since it is able to produce Sucrose (used for transportation and stockage) and both ADP-Glucose and UDP-Glucose. It is one of the only four proteins able to synthesize or cleave the Sucrose, and the only one able to catalyze it in both direction <ref>Salerno GL, Curatti L
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This enzyme has a fundamental role in the sucrose flow regulation since it is able to produce sucrose (used for transportation and stockage) and both ADP-glucose and UDP-glucose. It is one of the only four proteins able to synthesize or cleave the sucrose, and the only one able to catalyze it in both direction <ref>Salerno GL, Curatti L
Origin of sucrose metabolism in higher plants: when, how and why?
Origin of sucrose metabolism in higher plants: when, how and why?
Trends Plant Sci. 2003 Feb
Trends Plant Sci. 2003 Feb
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</ref>, thereby Sucrose synthase is implied in many pathways including cell wall, starch and glycoprotein synthesis <ref>Baroja-Fernández, E., Muñoz, F.J., Saikusa, T., Rodríguez-López, M., Akazawa, T. and Pozueta-Romero, J. Sucrose synthase catalyzes the de novo production of ADPglucose linked to starch biosynthesis in heterotrophic tissues of plants. Plant Cell Physiol.</ref>.
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</ref>, thereby Sucrose synthase is implied in many pathways including cell wall, starch and glycoprotein synthesis <ref>Baroja-Fernández, E., Muñoz, F.J., Saikusa, T., Rodríguez-López, M., Akazawa, T. and Pozueta-Romero, J. Sucrose synthase catalyzes the de novo production of ADP-glucose linked to starch biosynthesis in heterotrophic tissues of plants. Plant Cell Physiol.</ref>.
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Sucrose synthase catalyses the cleavage reaction at pH around 7 and the synthesis reaction at pH above 9. Cytoplasmic pH is around 6,5-7, it suggests that SUS works in vivo only to cleave sucrose, which explain why SUS1 is mostly in sink organs. Therefore, it is a linker between all the pathways that use or synthesize sucrose. SUS is involved in biomass production, nitrogen fixation, fruit and seed maturation and can response to stress (cold, anaerobic conditions, drought or gene induction).
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Sucrose synthase catalyses the cleavage reaction at pH around 7 and the synthesis reaction at pH above 9. Cytoplasmic pH is around 6,5-7, it suggests that SUS works ''in vivo'' only to cleave sucrose, which explain why SUS1 is mostly in sink organs. Therefore, it is a linker between all the pathways that use or synthesize sucrose. SUS is involved in biomass production, nitrogen fixation, fruit and seed maturation and can response to stress (cold, anaerobic conditions, drought or gene induction).
However, the binding to target mechanism is unknown at the molecular level.
However, the binding to target mechanism is unknown at the molecular level.
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In a mutant SUS1, we observe a decrease in amidon and lipids concentration, a misbalance between hexose and sucrose, and a perturbation of the organic acids synthesis (citrate and malate), during seed maturation
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In a mutant ''Sus1'' (SUS1 gene repression), we observe a decrease in amidon and lipids concentration, a misbalance between hexose and sucrose, and a perturbation of the organic acids synthesis (citrate and malate), during seed maturation
<ref>11 Juan Gabriel Angeles N_U ~Nez. Study of sucrose synthase in arabdopsis seed : lacalization,
<ref>11 Juan Gabriel Angeles N_U ~Nez. Study of sucrose synthase in arabdopsis seed : lacalization,
regulation and function. Sciences of the U.</ref>.
regulation and function. Sciences of the U.</ref>.
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Each monomer is a chain of 808 residues which possesses four specific domains:
Each monomer is a chain of 808 residues which possesses four specific domains:
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• 1-127: N-Terminal regulatory domain involved in targeting (Cellular Targeting Domain) <ref>Determination of structural requirements and probable regulatory effectors for membrane association of maize sucrose synthase 1. Hardin SC, Duncan KA, Huber SC. Plant Physiol. 2006</ref>. On this sequence, two serines can be phosphorylated, which enable a control of enzyme location <ref>Phosphorylation of sucrose synthase at serine 170: occurrence and possible role as a signal for proteolysis. Hardin SC, Tang GQ, Scholz A, Holtgraewe D, Winter H, Huber SC. Plant J. 2003</ref>.
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• 1-127: N-Terminal regulatory domain involved in targeting (Cellular Targeting Domain) <ref>Determination of structural requirements and probable regulatory effectors for membrane association of maize Sucrose Synthase 1. Hardin SC, Duncan KA, Huber SC. Plant Physiol. 2006</ref>. On this sequence, two serines can be phosphorylated, which enable a control of enzyme location <ref>Phosphorylation of Sucrose Synthase at serine 170: occurrence and possible role as a signal for proteolysis. Hardin SC, Tang GQ, Scholz A, Holtgraewe D, Winter H, Huber SC. Plant J. 2003</ref>.
• 157-276: EPBD: ENOD40 peptide-binding domain. This domain has a role in the regulation of the enzyme. It is able to bind a potassium ion.
• 157-276: EPBD: ENOD40 peptide-binding domain. This domain has a role in the regulation of the enzyme. It is able to bind a potassium ion.
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The active site of SUS1 is able to bind both fructose and UDP-glucose. UDP-glucose is mainly bound by the GT-BC domain, whereas the fructose in β-furanose form is bound within a pocket in the GT-Bn domain.
The active site of SUS1 is able to bind both fructose and UDP-glucose. UDP-glucose is mainly bound by the GT-BC domain, whereas the fructose in β-furanose form is bound within a pocket in the GT-Bn domain.
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The GT-B domain is highly conserved in other isoforms and in the sucrose-phosphate synthase. This conservation reinforce the evolutionary relationship of those enzymes. Furthermore, this domain is also conserved in other species.
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The GT-B domain is highly conserved in other isoforms and in the Sucrose-Phosphate Synthase. This conservation reinforce the evolutionary relationship of those enzymes. Furthermore, this domain is also conserved in other species.
== Regulation ==
== Regulation ==
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Sucrose synthase regulation is not well known, but here are some of the supposed mechanisms.
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Sucrose Synthase regulation is not well known, but here are some of the supposed mechanisms.
• ENOD40-A is a small hormon-like peptide able to specifically thiolates the Cys-266 of AtSUS1. It also inhibit the phosphorylation of Ser-167.
• ENOD40-A is a small hormon-like peptide able to specifically thiolates the Cys-266 of AtSUS1. It also inhibit the phosphorylation of Ser-167.
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• In Arabidopsis, SUS1 gene is probably regulated by both by sucrose and D-Glucose.
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• In Arabidopsis, SUS1 gene is probably regulated by both by sucrose and D-glucose.
• Conformational changes of the EPBD may change the active site activity through distortions of an α helix.
• Conformational changes of the EPBD may change the active site activity through distortions of an α helix.
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• The CTD can possibly interact with actin and other cellular target, which can regulate sucrose synthase activity.
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• The CTD can possibly interact with actin and other cellular target, which can regulate Sucrose Synthase activity.
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• In other organisms, it has been shown that the sucrose synthase is active into its dimer form, it is supposed to be the same phenomenon in ''Arabidopsis thaliana'', though it has not been prouved.
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• In other organisms, it has been shown that the Sucrose Synthase is active into its dimer form, it is supposed to be the same phenomenon in ''Arabidopsis thaliana'', though it has not been prouved.
</StructureSection>
</StructureSection>

Revision as of 14:37, 30 January 2016

This Sandbox is Reserved from 15/12/2015, through 15/06/2016 for use in the course "Structural Biology" taught by Bruno Kieffer at the University of Strasbourg, ESBS. This reservation includes Sandbox Reserved 1120 through Sandbox Reserved 1159.
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Structure and Functional aspects of Sucrose Synthase 1 from Arabidopsis thaliana

Sucrose Synthase 1 (EC:2.4.1.13), also known as the sucrose-UDP glucolsyltransferase 1, is a reversible enzyme allowing the synthesis or the degradation of sucrose in Arabidopsis thaliana. It is a 360 kDa tetramer and belongs to the Glycosyltransferase subfamily 4 (GT4).

X-ray crystal structures of AtSus1, as a complex with UDP-glucose at 2.8-Å resolution and as a complex with UDP and fructose at 2.85-Å resolution

Drag the structure with the mouse to rotate


References

• UniProt entry: P49040

• Brenda entry : 2.4.1.13

  1. ↑ Salerno GL, Curatti L Origin of sucrose metabolism in higher plants: when, how and why? Trends Plant Sci. 2003 Feb
  2. ↑ Baroja-Fernández, E., Muñoz, F.J., Saikusa, T., Rodríguez-López, M., Akazawa, T. and Pozueta-Romero, J. Sucrose synthase catalyzes the de novo production of ADP-glucose linked to starch biosynthesis in heterotrophic tissues of plants. Plant Cell Physiol.
  3. ↑ 11 Juan Gabriel Angeles N_U ~Nez. Study of sucrose synthase in arabdopsis seed : lacalization, regulation and function. Sciences of the U.
  4. ↑ Sucrose synthase oligomerization and F-actin association are regulated by sucrose concentration and phosphorylation. Duncan KA, Huber SC. Plant Cell Physiol. 2007 Nov; 48(11):1612-23.
  5. ↑ Salerno GL, Curatti L. Origin of sucrose metabolism in higher plants: when, how and why? Trends Plant Sci. 2003 Feb
  6. ↑ Determination of structural requirements and probable regulatory effectors for membrane association of maize Sucrose Synthase 1. Hardin SC, Duncan KA, Huber SC. Plant Physiol. 2006
  7. ↑ Phosphorylation of Sucrose Synthase at serine 170: occurrence and possible role as a signal for proteolysis. Hardin SC, Tang GQ, Scholz A, Holtgraewe D, Winter H, Huber SC. Plant J. 2003
  8. ↑ Glycosyltransferases: structures, functions, and mechanisms. Lairson LL, Henrissat B, Davies GJ, Withers SG. Annu Rev Biochem. 2008
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