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Characterization at the Molecular Level using Robust Biochemical Approaches of a New Kinase Protein
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Regulation of Chk1 by its C-terminal domain

Ana Kosoy1, Matthew J O'Connell

  • 1Department of Oncological Sciences, Mount Sinai School of Medicine, New York, NY 10029, USA.

Molecular Biology of the Cell
|August 22, 2008
PubMed

Insights

The C-terminal domain of Checkpoint kinase 1 (Chk1) is essential for its in vivo function, contrary to previous assumptions of autoinhibition. Specific mutations in this domain activate Chk1, revealing its critical role in kinase activity regulation.

Area of Science:

  • Molecular Biology
  • Cell Cycle Regulation
  • DNA Damage Response

Background:

  • Checkpoint kinase 1 (Chk1) is a key effector in the G2 DNA damage checkpoint.
  • The C-terminal domain of Chk1 contains ATM/R kinase phosphorylation sites, but its activation mechanism is unclear.
  • Previous studies suggested the C-terminal domain might possess autoinhibitory activity, as the isolated kinase domain is more active in vitro.

Purpose of the Study:

  • To investigate the role of the C-terminal domain in Chk1 activation and function.
  • To determine if the C-terminal domain is autoinhibitory or essential for activity.
  • To identify mutations that modulate Chk1 activity and understand their mechanism.

Main Methods:

  • Truncation and mutation of the Chk1 C-terminal domain.
  • In vivo functional assays of Chk1 activity.
  • Analysis of ectopically expressed and endogenously expressed Chk1 alleles.
  • Identification of intragenic suppressors of activated Chk1 alleles.

Main Results:

  • Truncation of the C-terminal domain inactivates Chk1 in vivo.
  • Mutations within the C-terminal domain can activate Chk1 independently of activating phosphorylation.
  • Activated Chk1 alleles exhibit temperature-sensitive loss of function when expressed endogenously.
  • Suppressor mutations map to the catalytic domain regions interacting with the C-terminus.

Conclusions:

  • The C-terminal domain of Chk1 is not autoinhibitory but is critical for adopting an active conformation.
  • The C-terminus plays a crucial role in regulating Chk1 activity in vivo.
  • These findings redefine the understanding of Chk1 regulation and its role in DNA damage response.

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