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== Function ==
== Function ==
The Sucrose Synthase is able to catalyse the following reaction in both directions:
The Sucrose Synthase is able to catalyse the following reaction in both directions:
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[[Image:Susy_reaction.jpg]]
[[Image:Susy_reaction.jpg]]
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This reaction is a nucleophilic substitution involving a glycosyl intermediate. The glucose is transfered between UDP (donor) and fructose (acceptor).
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It 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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• 277-776 : GT-B glycosyltransferase domain. It contains the catalytic site and presents a characteristic Rossman-folding
• 277-776 : GT-B glycosyltransferase domain. It contains the catalytic site and presents a characteristic Rossman-folding
<ref>Glycosyltransferases: structures, functions, and mechanisms. Lairson LL, Henrissat B, Davies GJ, Withers SG. Annu Rev Biochem. 2008
<ref>Glycosyltransferases: structures, functions, and mechanisms. Lairson LL, Henrissat B, Davies GJ, Withers SG. Annu Rev Biochem. 2008
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</ref>
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</ref>. It is divided in two parts, the GT-BN and the GT-BC.
• 776-808 : C-terminal extension. The length of this domain is variable depending of the SUS isoform.
• 776-808 : C-terminal extension. The length of this domain is variable depending of the SUS isoform.
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The SUS1 tetramer is flat, with two types of subunit interfaces, the A:B and A:D interfaces. The A:D interface is an interaction between the C-terminal extension and the linker, whereas the A:B interface is created by the interaction of adjacent EPBD domains.
The SUS1 tetramer is flat, with two types of subunit interfaces, the A:B and A:D interfaces. The A:D interface is an interaction between the C-terminal extension and the linker, whereas the A:B interface is created by the interaction of adjacent EPBD domains.
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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
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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 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.
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.

Revision as of 13:38, 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 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

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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 ADPglucose linked to starch biosynthesis in heterotrophic tissues of plants. Plant Cell Physiol.
  3. ↑ 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.
  4. ↑ Salerno GL, Curatti L. Origin of sucrose metabolism in higher plants: when, how and why? Trends Plant Sci. 2003 Feb
  5. ↑ 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
  6. ↑ 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
  7. ↑ Glycosyltransferases: structures, functions, and mechanisms. Lairson LL, Henrissat B, Davies GJ, Withers SG. Annu Rev Biochem. 2008
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