Cytosolic glutamine synthetase and not nitrate reductase from the green alga Chlamydomonas reinhardtii is phosphorylated and binds 14-3-3 proteins.
The nitrate reductase activity from Chlamydomonas reinhardtii was not altered when extracts were incubated with yeast 14-3-3 proteins in the presence of Mg-ATP. However, the C. reinhardtii extracts contained 14-3-3 proteins capable of inhibiting the spinach nitrate reductase, raising the question of their physiological substrates. Two C. reinhardtii proteins of about 48 and 35 kDa were eluted from 14-3-3 affinity chromatography columns and bound to 14-3-3s in overlay assays. The 48-kDa protein corresponded to the cytosolic isoform of glutamine synthetase (GS1). The GSI was phosphorylated by a Ca2+-and calmodulin-dependent protein kinase partially purified from the alga. However, neither phosphorylation nor 14-3-3 binding seemed to change GS catalytic activity.
Pozuelo
M
M
Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, Spain.
MacKintosh
C
C
Galván
A
A
Fernández
E
E
D048948:14-3-3 Proteins; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D048948:14-3-3 Proteins; D014446:Tyrosine 3-Monooxygenase; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D005974:Glutamate-Ammonia Ligase