Similar protein phosphatases control starch metabolism in plants and glycogen metabolism in mammals.
We report that protein phosphorylation is involved in the control of starch metabolism in Arabidopsis leaves at night. sex4 (starch excess 4) mutants, which have strongly reduced rates of starch metabolism, lack a protein predicted to be a dual specificity protein phosphatase. We have shown that this protein is chloroplastic and can bind to glucans and have presented evidence that it acts to regulate the initial steps of starch degradation at the granule surface. Remarkably, the most closely related protein to SEX4 outside the plant kingdom is laforin, a glucan-binding protein phosphatase required for the metabolism of the mammalian storage carbohydrate glycogen and implicated in a severe form of epilepsy (Lafora disease) in humans.
Niittylä
Totte
T
Department of Metabolic Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom.
Comparot-Moss
Sylviane
S
Lue
Wei-Ling
WL
Messerli
Gaëlle
G
Trevisan
Martine
M
Seymour
Michael D J
MD
Gatehouse
John A
JA
Villadsen
Dorthe
D
Smith
Steven M
SM
Chen
Jychian
J
Zeeman
Samuel C
SC
Smith
Alison M
AM
D000818:Animals; D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000737:chemistry; D005936:Glucans / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D008322:Mammals / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D018515:Plant Leaves / Q000737:chemistry / Q000166:cytology; D013213:Starch / Q000378:metabolism*
D029681:Arabidopsis Proteins; D005936:Glucans; D013213:Starch; D006003:Glycogen; D010749:Phosphoprotein Phosphatases