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J Biol Chem. 2014 May 30;289(22):15631-41. doi: 10.1074/jbc.M113.534768. Epub 2014 Apr 10.

Diversity in guanosine 3',5'-bisdiphosphate (ppGpp) sensitivity among guanylate kinases of bacteria and plants.

Author information

1
From the Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan, the Proteo-Science Center and the Venture Business Laboratory, Ehime University, Matsuyama 790-8577, Japan.
2
the Proteo-Science Center and the Venture Business Laboratory, Ehime University, Matsuyama 790-8577, Japan.
3
the Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
4
the Faculty of Agriculture, Ehime University, Matsuyama 790-8566, Japan.
5
the Institute for Plant Biochemistry, Cluster of Excellence on Plant Sciences, Heinrich-Heine University, Düsseldorf D-40225, Germany.
6
the Proteo-Science Center and the Venture Business Laboratory, Ehime University, Matsuyama 790-8577, Japan, tozawa.yuzuru.mx@ehime-u.ac.jp.

Abstract

The guanosine 3',5'-bisdiphosphate (ppGpp) signaling system is shared by bacteria and plant chloroplasts, but its role in plants has remained unclear. Here we show that guanylate kinase (GK), a key enzyme in guanine nucleotide biosynthesis that catalyzes the conversion of GMP to GDP, is a target of regulation by ppGpp in chloroplasts of rice, pea, and Arabidopsis. Plants have two distinct types of GK that are localized to organelles (GKpm) or to the cytosol (GKc), with both enzymes being essential for growth and development. We found that the activity of rice GKpm in vitro was inhibited by ppGpp with a Ki of 2.8 μM relative to the substrate GMP, whereas the Km of this enzyme for GMP was 73 μM. The IC50 of ppGpp for GKpm was ∼10 μM. In contrast, the activity of rice GKc was insensitive to ppGpp, as was that of GK from bakers' yeast, which is also a cytosolic enzyme. These observations suggest that ppGpp plays a pivotal role in the regulation of GTP biosynthesis in chloroplasts through specific inhibition of GKpm activity, with the regulation of GTP biosynthesis in chloroplasts thus being independent of that in the cytosol. We also found that GKs of Escherichia coli and Synechococcus elongatus PCC 7942 are insensitive to ppGpp, in contrast to the ppGpp sensitivity of the Bacillus subtilis enzyme. Our biochemical characterization of GK enzymes has thus revealed a novel target of ppGpp in chloroplasts and has uncovered diversity among bacterial GKs with regard to regulation by ppGpp.

KEYWORDS:

Bacteria; Chloroplast; Enzymes; Guanylate Kinase; Metabolism; Nucleoside Nucleotide Biosynthesis; Oryza Sativa; Plant; Stringent Response; ppGpp

PMID:
24722991
PMCID:
PMC4140918
DOI:
10.1074/jbc.M113.534768
[Indexed for MEDLINE]
Free PMC Article

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