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Phosphorylation of Arabidopsis transketolase at Ser428 provides a potential paradigm for the metabolic control of chloroplast carbon metabolism.

Biochem. J.2014 Mar 01;458(2):313-22
Agostinho G Rocha 1 , Norbert Mehlmer 1 , Simon Stael 2 , Andrea Mair 3 , Nargis Parvin 1 , Fatima Chigri 4 , Markus Teige , Ute C Vothknecht
Agostinho G Rocha 1 , Norbert Mehlmer 1 , Simon Stael 2 , Andrea Mair 3 , Nargis Parvin 1 , Fatima Chigri 4 , Markus Teige , Ute C Vothknecht
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Author information
  • 1 *Department of Biology I, LMU Munich, Groβhaderner Str. 2-4, D-82152 Planegg-Martinsried, Germany.
  • 2 †Department of Biochemistry, MFPL, University of Vienna, Dr. Bohr Gasse 9/5, A-1030 Vienna, Austria.
  • 3 ‡Department of Molecular Systems Biology (MoSys), University of Vienna, Althanstr. 14, A-1090 Vienna, Austria.
  • 4 §Center for Integrated Protein Science (Munich), Department of Biology, LMU Munich, D-82152 Martinsried, Germany.
全文

摘要


Calcium is an important second messenger in eukaryotic cells that regulates many different cellular processes. To elucidate calcium regulation in chloroplasts, we identified the targets of calcium-dependent phosphorylation within the stromal proteome. A 73 kDa protein was identified as one of the most dominant proteins undergoing phosphorylation in a calcium-dependent manner in the stromal extracts of both Arabidopsis and Pisum. It was identified as TKL (transketolase), an essential enzyme of both the Calvin-Benson-Bassham cycle and the oxidative pentose phosphate pathway. Calcium-dependent phosphorylation of both Arabidopsis isoforms (AtTKL1 and AtTKL2) could be confirmed in vitro using recombinant proteins. The phosphorylation is catalysed by a stroma-localized protein kinase, which cannot utilize GTP. Phosphorylation of AtTKL1, the dominant isoform in most tissues, occurs at a serine residue that is conserved in TKLs of vascular plants. By contrast, an aspartate residue is present in this position in cyanobacteria, algae and mosses. Characterization of a phosphomimetic mutant (S428D) indicated that Ser428 phosphorylation exerts significant effects on the enzyme's substrate saturation kinetics at specific physiological pH values. The results of the present study point to a role for TKL phosphorylation in the regulation of carbon allocation.