| Structural highlights
Function
[Q944A8_ARATH] Starch granule-associated phosphoglucan phosphatase involved in the control of starch accumulation. Acts as major regulator of the initial steps of starch degradation at the granule surface. Functions during the day by dephosphorylating the night-accumulated phospho-oligosaccharides. Can release phosphate from both the C6 and the C3 positions.[1] [2] [3] [4] [5] [6] [7] [8] [9]
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
Living organisms utilize carbohydrates as essential energy storage molecules. Starch is the predominant carbohydrate storage molecule in plants while glycogen is utilized in animals. Starch is a water-insoluble polymer that requires the concerted activity of kinases and phosphatases to solubilize the outer surface of the glucan and mediate starch catabolism. All known plant genomes encode the glucan phosphatase Starch Excess4 (SEX4). SEX4 can dephosphorylate both the starch granule surface and soluble phosphoglucans and is necessary for processive starch metabolism. The physical basis for the function of SEX4 as a glucan phosphatase is currently unclear. Herein, we report the crystal structure of SEX4, containing phosphatase, carbohydrate-binding, and C-terminal domains. The three domains of SEX4 fold into a compact structure with extensive interdomain interactions. The C-terminal domain of SEX4 integrally folds into the core of the phosphatase domain and is essential for its stability. The phosphatase and carbohydrate-binding domains directly interact and position the phosphatase active site toward the carbohydrate-binding site in a single continuous pocket. Mutagenesis of the phosphatase domain residue F167, which forms the base of this pocket and bridges the two domains, selectively affects the ability of SEX4 to function as a glucan phosphatase. Together, these results reveal the unique tertiary architecture of SEX4 that provides the physical basis for its function as a glucan phosphatase.
Structural basis for the glucan phosphatase activity of Starch Excess4.,Vander Kooi CW, Taylor AO, Pace RM, Meekins DA, Guo HF, Kim Y, Gentry MS Proc Natl Acad Sci U S A. 2010 Aug 31;107(35):15379-84. Epub 2010 Aug 2. PMID:20679247[10]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Niittyla T, Comparot-Moss S, Lue WL, Messerli G, Trevisan M, Seymour MD, Gatehouse JA, Villadsen D, Smith SM, Chen J, Zeeman SC, Smith AM. Similar protein phosphatases control starch metabolism in plants and glycogen metabolism in mammals. J Biol Chem. 2006 Apr 28;281(17):11815-8. Epub 2006 Mar 2. PMID:16513634 doi:10.1074/jbc.M600519200
- ↑ Kerk D, Conley TR, Rodriguez FA, Tran HT, Nimick M, Muench DG, Moorhead GB. A chloroplast-localized dual-specificity protein phosphatase in Arabidopsis contains a phylogenetically dispersed and ancient carbohydrate-binding domain, which binds the polysaccharide starch. Plant J. 2006 May;46(3):400-13. PMID:16623901 doi:10.1111/j.1365-313X.2006.02704.x
- ↑ Sokolov LN, Dominguez-Solis JR, Allary AL, Buchanan BB, Luan S. A redox-regulated chloroplast protein phosphatase binds to starch diurnally and functions in its accumulation. Proc Natl Acad Sci U S A. 2006 Jun 20;103(25):9732-7. Epub 2006 Jun 13. PMID:16772378 doi:10.1073/pnas.0603329103
- ↑ Hsu S, Kim Y, Li S, Durrant ES, Pace RM, Woods VL Jr, Gentry MS. Structural insights into glucan phosphatase dynamics using amide hydrogen-deuterium exchange mass spectrometry. Biochemistry. 2009 Oct 20;48(41):9891-902. doi: 10.1021/bi9008853. PMID:19754155 doi:10.1021/bi9008853
- ↑ Kotting O, Santelia D, Edner C, Eicke S, Marthaler T, Gentry MS, Comparot-Moss S, Chen J, Smith AM, Steup M, Ritte G, Zeeman SC. STARCH-EXCESS4 is a laforin-like Phosphoglucan phosphatase required for starch degradation in Arabidopsis thaliana. Plant Cell. 2009 Jan;21(1):334-46. doi: 10.1105/tpc.108.064360. Epub 2009 Jan 13. PMID:19141707 doi:10.1105/tpc.108.064360
- ↑ Hejazi M, Fettke J, Kotting O, Zeeman SC, Steup M. The Laforin-like dual-specificity phosphatase SEX4 from Arabidopsis hydrolyzes both C6- and C3-phosphate esters introduced by starch-related dikinases and thereby affects phase transition of alpha-glucans. Plant Physiol. 2010 Feb;152(2):711-22. doi: 10.1104/pp.109.149914. Epub 2009 Dec , 16. PMID:20018599 doi:10.1104/pp.109.149914
- ↑ Santelia D, Kotting O, Seung D, Schubert M, Thalmann M, Bischof S, Meekins DA, Lutz A, Patron N, Gentry MS, Allain FH, Zeeman SC. The phosphoglucan phosphatase like sex Four2 dephosphorylates starch at the C3-position in Arabidopsis. Plant Cell. 2011 Nov;23(11):4096-111. doi: 10.1105/tpc.111.092155. Epub 2011 Nov , 18. PMID:22100529 doi:10.1105/tpc.111.092155
- ↑ Weise SE, Aung K, Jarou ZJ, Mehrshahi P, Li Z, Hardy AC, Carr DJ, Sharkey TD. Engineering starch accumulation by manipulation of phosphate metabolism of starch. Plant Biotechnol J. 2012 Jun;10(5):545-54. doi: 10.1111/j.1467-7652.2012.00684.x., Epub 2012 Feb 9. PMID:22321580 doi:10.1111/j.1467-7652.2012.00684.x
- ↑ Vander Kooi CW, Taylor AO, Pace RM, Meekins DA, Guo HF, Kim Y, Gentry MS. Structural basis for the glucan phosphatase activity of Starch Excess4. Proc Natl Acad Sci U S A. 2010 Aug 31;107(35):15379-84. Epub 2010 Aug 2. PMID:20679247 doi:10.1073/pnas.1009386107
- ↑ Vander Kooi CW, Taylor AO, Pace RM, Meekins DA, Guo HF, Kim Y, Gentry MS. Structural basis for the glucan phosphatase activity of Starch Excess4. Proc Natl Acad Sci U S A. 2010 Aug 31;107(35):15379-84. Epub 2010 Aug 2. PMID:20679247 doi:10.1073/pnas.1009386107
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