Protein phosphorylation regulates maize endosperm starch synthase IIa activity and protein−protein interactions
Autor: | Sahar Mehrpouyan, Usha Menon, Michael J. Emes, Ian J. Tetlow |
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Rok vydání: | 2021 |
Předmět: |
0106 biological sciences
0301 basic medicine Starch Electrophoretic Mobility Shift Assay Plant Science Biology Zea mays 01 natural sciences Endosperm 03 medical and health sciences chemistry.chemical_compound Starch Synthase Genetics Immunoprecipitation Amyloplast Protein phosphorylation Plastids Phosphorylation Protein kinase A Glucans Polyacrylamide gel electrophoresis Plant Proteins chemistry.chemical_classification Cell Biology 030104 developmental biology Enzyme Biochemistry chemistry 010606 plant biology & botany |
Zdroj: | The Plant Journal. 105:1098-1112 |
ISSN: | 1365-313X 0960-7412 |
Popis: | Starch synthesis is an elaborate process employing several isoforms of starch synthases (SSs), starch branching enzymes (SBEs) and debranching enzymes (DBEs). In cereals, some starch biosynthetic enzymes can form heteromeric complexes whose assembly is controlled by protein phosphorylation. Previous studies suggested that SSIIa forms a trimeric complex with SBEIIb, SSI, in which SBEIIb is phosphorylated. This study investigates the post-translational modification of SSIIa, and its interactions with SSI and SBEIIb in maize amyloplast stroma. SSIIa, immunopurified and shown to be free from other soluble starch synthases, was shown to be readily phosphorylated, affecting Vmax but with minor effects on substrate Kd and Km values, resulting in a 12-fold increase in activity compared with the dephosphorylated enzyme. This ATP-dependent stimulation of activity was associated with interaction with SBEIIb, suggesting that the availability of glucan branching limits SSIIa and is enhanced by physical interaction of the two enzymes. Immunoblotting of maize amyloplast extracts following non-denaturing polyacrylamide gel electrophoresis identified multiple bands of SSIIa, the electrophoretic mobilities of which were markedly altered by conditions that affected protein phosphorylation, including protein kinase inhibitors. Separation of heteromeric enzyme complexes by GPC, following alteration of protein phosphorylation states, indicated that such complexes are stable and may partition into larger and smaller complexes. The results suggest a dual role for protein phosphorylation in promoting association and dissociation of SSIIa-containing heteromeric enzyme complexes in the maize amyloplast stroma, providing new insights into the regulation of starch biosynthesis in plants. |
Databáze: | OpenAIRE |
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