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Arabidopsis PDK1: identification of sites important for activity and downstream phosphorylation of S6 kinase

På svenska

Author

  • L Otterhag
  • N Gustavsson
  • Magnus Alsterfjord
  • Christophe Pical
  • H Lehrach
  • J Gobom
  • Marianne Sommarin

Summary, in English

The A rabidopsis thaliana protein kinase AtPDK1 was identified as a homologue of the mammalian 3-phosphoinositide-dependent protein kinase-1 (PDK1), which is involved in a number of physiological processes including cell growth and proliferation. We now show that AtPDK1 expressed in E. coli as a recombinant protein, undergoes autophosphorylation at several sites. Using mass spectrometry, three phosphorylated amino acid residues, Ser-177, Ser-276 and Ser-382, were identified, followed by mutational analyses to reveal their roles. These residues are not conserved in mammalian PDK1s. Mutation of Ser-276 in AtPDK1 to alanine resulted in an enzyme with no detectable autophosphorylation. Autophosphorylation was significantly reduced in the Ser177Ala mutant but was only slightly reduced in the Ser382Ala mutant. Other identified sites of importance for autophosphorylation and/or activity of AtPDK1 were Asp-167, Thr-176, and Thr-211. Sites in the mammalian PDK1 corresponding to Asp- 167 and Thr-211 are essential for PDK1 autophosphorylation and activity. Autophosphorylation was absent in the Asp167Ala mutant while the Thr176Ala and The211Ala mutants exhibited very low but detectable autophosphorylation, pointing to both similarity and difference between mammalian and plant enzymes. We also demonstrate that AtS6k2, an A. thaliana homologue to the mammalian S6 kinases, is an in vitro tar et of AtPDK1. Our data clearly show that Asp- 167, Thr-176, Ser-177, Thr-211, and Ser-276 in AtPDK1 are important for the downstream phosphorylation of AtS6k2. The results confirm that AtPDK1, like mammalian PDK1, needs phosphorylation at several sites for full downstream phosphorylation activity. Finally, we investigated A. thaliana 14-3-3 proteins as potential AtPDK1 regulatory proteins and the effect of phospholipids on the AtPDK1 activity. Nine of the 12 14-3-3 isoforms tested enhanced AtPDK1 activity whereas one isoform suppressed the activity. No significant effects on AtPDK1 activity by the various phospholipids (including phosphoinositides) were evident. (C) 2005 Elsevier SAS. All rights reserved.

Publishing year

2006

Language

English

Pages

11-21

Publication/Series

Biochimie

Volume

88

Issue

1

Document type

Journal article

Publisher

Elsevier

Topic

  • Biochemistry and Molecular Biology

Keywords

  • thaliana
  • Arabidopsis
  • AGC kinase
  • 14-3-3 protein
  • autophosphorylation
  • AtS6k2

Status

Published

ISBN/ISSN/Other

  • ISSN: 1638-6183