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Amide Hydrogen/Deuterium Exchange & MALDI-TOF Mass Spectrometry Analysis of Pak2 Activation
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Group I and II mammalian PAKs have different modes of activation by Cdc42

Yohendran Baskaran1, Yuen-Wai Ng, Widyawilis Selamat

  • 1sGSK group, Astar Neuroscience Research Partnership, Proteos Building, 61 Biopolis Drive, Singapore 138673, Singapore.

EMBO Reports
|June 2, 2012
PubMed

Insights

The p21-activated kinase 4 (PAK4) is regulated by an auto-inhibitory domain (AID), not activation loop phosphorylation. Cdc42 binding to PAK4 releases this inhibition, controlling its activity.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Kinase Regulation

Background:

  • p21-activated kinases (PAKs) are crucial Cdc42 effectors involved in various cellular processes.
  • PAKs are classified into Group I (PAK1-like) and Group II (PAK4-like) kinases.
  • The regulatory mechanism of human PAK4, a widely expressed kinase, remained largely unknown.

Purpose of the Study:

  • To elucidate the regulatory mechanism of human PAK4.
  • To identify the specific domain responsible for PAK4 auto-inhibition.
  • To understand the role of Cdc42 binding in PAK4 activation.

Main Methods:

  • Identification and characterization of the auto-inhibitory domain (AID) of PAK4.
  • Analysis of PAK4 phosphorylation status, particularly on Ser474 in the activation loop.
  • Investigation of the effect of Cdc42 binding on PAK4 activity and conformation.

Main Results:

  • A novel auto-inhibitory domain (AID), comprising amino acids 20-68, was identified in PAK4.
  • PAK4 exhibits constitutive phosphorylation on Ser474 within the activation loop.
  • PAK4 remains inactive until binding with Cdc42, which relieves inhibition mediated by the AID.

Conclusions:

  • Group II PAKs, including PAK4, are primarily regulated by conformational changes induced by the AID.
  • Unlike Group I PAKs, PAK4 activation is not dependent on A-loop phosphorylation but on the release of AID-mediated inhibition.
  • This study reveals a distinct regulatory mechanism for Group II PAKs, highlighting the importance of the AID in controlling PAK4 activity.

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