Planta

, Volume 213, Issue 3, pp 396–401 | Cite as

The chloroplastic glutamine synthetase (GS-2) of tobacco is phosphorylated and associated with 14-3-3 proteins inside the chloroplast

Original Article

Abstract.

The chloroplastic isoform of glutamine synthetase (GS-2, EC 6.3.1.2) from Nicotiana tabacum L. is phosphorylated at the serine residues. At least three of the six GS-2 subunits separated by two-dimensional polyacrylamide gel electrophoresis cross-reacted with an antibody raised against phosphoserine. This provoked the question as to whether 14-3-3 proteins might be present in the chloroplast and bind to chloroplastic GS-2. Although two different 14-3-3 proteins of 32 and 30 kDa were present in total leaf extracts, in the soluble fraction of chloroplasts, only the 32-kDa 14-3-3 protein was immunodetected with an antibody raised against a conserved region of 14-3-3 protein from corn. This demonstrates the presence of a chloroplast-located isoform of 14-3-3 proteins in tobacco. To examine a putative binding of GS-2 to these 14-3-3 proteins in vivo, the native GS-2 holoenzyme was probed with a 14-3-3 antibody. The strong cross-reaction between GS-2 and the 14-3-3 antibody clearly points to a binding of GS-2 and 14-3-3 in tobacco chloroplasts. Only those oligomers of GS-2 that were strongly associated with 14-3-3 proteins were catalytically active.

14-3-3 proteins Chloroplast Glutamine synthetase Nicotiana (14-3-3 proteins) Phosphoserine 

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Copyright information

© Springer-Verlag 2001

Authors and Affiliations

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    • 1
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    • 1
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    • 2
  1. 1.Albrecht-von-Haller-Institut für Pflanzenwissenschaften, Untere Karspüle 2, 37073 Göttingen, Germany
  2. 2.Plant Nutrition Laboratory, Department of Agricultural Sciences, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871 Frederiksberg C, Copenhagen, Denmark

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