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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

Drag the structure with the mouse to rotate

71/719877/Susy/3

Function

The Sucrose Synthase is able to catalyse the following reaction in both directions:

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 ^[1], thereby Sucrose synthase is implied in many pathways including cell wall, starch and glycoprotein synthesis ^[2].

Sucrose synthase catalyses the cleavage reaction at pH around 7 and the synthesis reaction at pH above 9. 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.

Structural highlights

Sucrose synthase is normally a homotetrameric enzyme, but it can also exist in a dimer form ^[3]. There are 6 SUS isoforms in Arabidopsis thaliana and all of them are structurally similar to sucrose phosphate synthases and glycogen synthases. ^[4]. Each monomer is a chain of 808 residues which possesses four specific domains:

• 1-127: N-Terminal regulatory domain involved in targeting ^[5]. On this sequence, two serines can be phosphorylated, which enable a control of enzyme location ^[6].

• 1-127: CTD: Cellular targeting domain.

• 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.

• 277-776 : GT-B glycosyltransferase domain. It contains the catlytic site and presents a characteristic Rossman-folding

^[7]

• 776-808 : C-terminal extension. The length of this domain is variable depending of the SUS isoform.

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 adjascents EPBD domains.

The active site of SUS1 is able to bind both UDP-fructose and UDP-glucose.

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

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.

References

• UniProt entry: P49040

• Brenda entry : 2.4.1.13

↑ Salerno GL, Curatti L Origin of sucrose metabolism in higher plants: when, how and why? Trends Plant Sci. 2003 Feb
↑ 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.
↑ 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.
↑ Salerno GL, Curatti L. Origin of sucrose metabolism in higher plants: when, how and why? Trends Plant Sci. 2003 Feb
↑ 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
↑ 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
↑ Glycosyltransferases: structures, functions, and mechanisms. Lairson LL, Henrissat B, Davies GJ, Withers SG. Annu Rev Biochem. 2008

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Sandbox Reserved 1136

From Proteopedia

Revision as of 12:36, 30 January 2016

Structure and Functional aspects of Sucrose Synthase from Arabidopsis thaliana

Function

Structural highlights

Regulation

References

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@@ Line 41: / Line 41: @@
 [[Image:Monomer_structure.jpg]]
+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 adjascents EPBD domains.
+The active site of SUS1 is able to bind both UDP-fructose and UDP-glucose.
 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 ==
+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.
 </StructureSection>