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The mechanism of PAK activation. Autophosphorylation events in both regulatory and kinase domains control activity

C Chong1, L Tan, L Lim

  • 1Glaxo-IMCB Group, Institute of Molecular and Cell Biology, 30 Medical Dr., Singapore 117609.

The Journal of Biological Chemistry
|March 30, 2001
PubMed

Insights

p21-activated kinases (PAKs) activation is modulated by autophosphorylation. Specific sites in the kinase inhibitory domain are crucial for PAK activation, while others regulate interactions with focal complexes.

Area of Science:

  • Cellular signaling
  • Protein kinase regulation

Background:

  • p21-activated kinases (PAKs) are crucial signaling enzymes.
  • PAKs undergo autophosphorylation upon activation by factors like Cdc42.
  • Autophosphorylation influences PAK's interaction with regulatory partners.

Purpose of the Study:

  • To investigate the role of specific autophosphorylation sites in PAK catalytic activity.
  • To differentiate the mechanisms of PAK activation by Cdc42 and sphingosine.

Main Methods:

  • In vivo and in vitro analyses of alpha- and betaPAK.
  • Site-directed mutagenesis to alter autophosphorylation sites.
  • Assessment of kinase catalytic activity and protein-protein interactions.

Main Results:

  • Most N-terminal regulatory domain phosphorylations do not directly activate PAK.
  • Phosphorylation of alphaPAK serine 144 or betaPAK serine 139 significantly contributes to activation.
  • Sphingosine-mediated activation is independent of these specific serine residues.
  • Three other autophosphorylation sites control association with focal complexes via PIX and Nck.

Conclusions:

  • Specific autophosphorylation sites in the kinase inhibitory domain are key drivers of PAK activation.
  • PAK exhibits distinct activation pathways, with Cdc42-induced activation relying on specific serine residues, unlike sphingosine-mediated activation.
  • Autophosphorylation plays a dual role in regulating both catalytic activity and protein complex formation.

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