@article{ComparotMossKoettingStettleretal.2010,
  author    = {Comparot-Moss, Sylviane and Koetting, Oliver and Stettler, Michaela and Edner, Christoph and Graf, Alexander and Weise, Sean E. and Streb, Sebastian and Lue, Wei-Ling and MacLean, Daniel and Mahlow, Sebastian and Ritte, Gerhard and Steup, Martin and Chen, Jychian and Zeeman, Samuel C. and Smith, Alison M.},
  title     = {A putative phosphatase, LSF1, is required for normal starch turnover in Arabidopsis leaves},
  issn      = {0032-0889},
  doi       = {10.1104/pp.109.148981},
  year      = {2010},
  abstract  = {A putative phosphatase, LSF1 (for LIKE SEX4; previously PTPKIS2), is closely related in sequence and structure to STARCH-EXCESS4 (SEX4), an enzyme necessary for the removal of phosphate groups from starch polymers during starch degradation in Arabidopsis (Arabidopsis thaliana) leaves at night. We show that LSF1 is also required for starch degradation: lsf1 mutants, like sex4 mutants, have substantially more starch in their leaves than wild-type plants throughout the diurnal cycle. LSF1 is chloroplastic and is located on the surface of starch granules. lsf1 and sex4 mutants show similar, extensive changes relative to wild-type plants in the expression of sugar-sensitive genes. However, although LSF1 and SEX4 are probably both involved in the early stages of starch degradation, we show that LSF1 neither catalyzes the same reaction as SEX4 nor mediates a sequential step in the pathway. Evidence includes the contents and metabolism of phosphorylated glucans in the single mutants. The sex4 mutant accumulates soluble phospho- oligosaccharides undetectable in wild-type plants and is deficient in a starch granule-dephosphorylating activity present in wild-type plants. The lsf1 mutant displays neither of these phenotypes. The phenotype of the lsf1/sex4 double mutant also differs from that of both single mutants in several respects. We discuss the possible role of the LSF1 protein in starch degradation.},
  language  = {en}
}
@article{KoettingSanteliaEdneretal.2009,
  author    = {Koetting, Oliver and Santelia, Diana and Edner, Christoph and Eicke, Simona and Marthaler, Tina and Gentry, Matthew S. and Comparot-Moss, Sylviane and Chen, Jychian and Smith, Alison M. and Steup, Martin and Ritte, Gerhard and Zeeman, Samuel C.},
  title     = {STARCH-EXCESS4 is a laforin-like phosphoglucan phosphatase required for starch degradation in Arabidopsis thaliana},
  issn      = {1040-4651},
  doi       = {10.1105/tpc.108.064360},
  year      = {2009},
  abstract  = {Starch is the major storage carbohydrate in plants. It is comprised of glucans that form semicrystalline granules. Glucan phosphorylation is a prerequisite for normal starch breakdown, but phosphoglucan metabolism is not understood. A putative protein phosphatase encoded at the Starch Excess 4 (SEX4) locus of Arabidopsis thaliana was recently shown to be required for normal starch breakdown. Here, we show that SEX4 is a phosphoglucan phosphatase in vivo and define its role within the starch degradation pathway. SEX4 dephosphorylates both the starch granule surface and soluble phosphoglucans in vitro, and sex4 null mutants accumulate phosphorylated intermediates of starch breakdown. These compounds are linear alpha-1,4-glucans esterified with one or two phosphate groups. They are released from starch granules by the glucan hydrolases alpha-amylase and isoamylase. In vitro experiments show that the rate of starch granule degradation is increased upon simultaneous phosphorylation and dephosphorylation of starch. We propose that glucan phosphorylating enzymes and phosphoglucan phosphatases work in synergy with glucan hydrolases to mediate efficient starch catabolism.},
  language  = {en}
}
@article{LiFranciscoZhouetal.2009,
  author    = {Li, Jing and Francisco, Perigio and Zhou, Wenxu and Edner, Christoph and Steup, Martin and Ritte, Gerhard and Bond, Charles S. and Smith, Steven M.},
  title     = {Catalytically-inactive beta-amylase BAM4 required for starch breakdown in Arabidopsis leaves is a starch- binding-protein},
  issn      = {0003-9861},
  doi       = {10.1016/j.abb.2009.07.024},
  year      = {2009},
  abstract  = {Of the four chloroplast beta-amylase (BAM) proteins identified in Arabidopsis, BAM3 and BAM4 were previously shown to play the major roles in leaf starch breakdown, although BAM4 apparently lacks key active site residues and beta- amylase activity. Here we tested multiple BAM4 proteins with different N-terminal sequences with a range of glucan substrates and assay methods, but detected no alpha-1,4-glucan hydrolase activity. BAM4 did not affect BAM1, BAM2 or BAM3 activity even when added in 10-fold excess, nor the BAM3-catalysed release of maltose from isolated starch granules in the presence of glucan water dikinase. However, BAM4 binds to amylopectin and to amylose-Sepharose whereas BAM2 has very low beta-amylase activity and poor glucan binding. The low activity of BAM2 may be explained by poor glucan binding but absence of BAM4 activity is not. These results suggest that BAM4 facilitates starch breakdown by a mechanism involving direct interaction with starch or other alpha-1,4-glucan.},
  language  = {en}
}