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Related Experiment Videos

Substrate sequestration by a proteolytically inactive Lon mutant.

L Van Melderen1, S Gottesman

  • 1Laboratory of Molecular Biology, National Cancer Institute, Bethesda, MD 20892-4255, USA.

Proceedings of the National Academy of Sciences of the United States of America
|May 26, 1999
PubMed
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The Escherichia coli Lon protease, when mutated, can sequester unstable proteins like SulA instead of degrading them. This binding, rather than degradation, rescues cells from UV damage and capsule overproduction, revealing a dual function for Lon.

Area of Science:

  • Molecular biology
  • Biochemistry
  • Cellular biology

Background:

  • The Lon protein in Escherichia coli is an ATP-dependent protease crucial for degrading abnormal and unstable proteins.
  • Key substrates include SulA (a cell division inhibitor) and RcsA (a transcriptional regulator).
  • Lon functions as a multimer with ATPase and serine active sites.

Purpose of the Study:

  • To investigate the role of the Lon protease's active site and ATPase motif in its function.
  • To understand the mechanism of substrate degradation and its impact on cellular processes.
  • To explore potential non-degradative functions of Lon.

Main Methods:

  • Overexpression of wild-type and mutated Lon proteins (LonS679A and ATPase mutants) in a lon deletion mutant of Escherichia coli.

Related Experiment Videos

  • Assessment of cellular phenotypes, including UV sensitivity and capsule production.
  • Analysis of SulA protein stability and degradation in the presence of wild-type and mutant Lon.

    • Main Results:

    • Overexpression of LonS679A (mutated active site) complemented lon deletion mutant phenotypes (UV sensitivity, capsule overproduction) without degrading SulA.
    • LonS679A protected SulA from degradation by other proteases, suggesting substrate binding and sequestration.
    • Mutations in the ATPase site abolished Lon's ability to complement the lon deletion mutant, irrespective of the active site serine.

    Conclusions:

    • The Lon protease can sequester substrates without degrading them, leading to apparent complementation of cellular defects.
    • ATP-dependent unfolding and translocation into protected chambers are likely key steps in Lon-mediated degradation.
    • Mutant Lon proteins highlight a dual role in substrate sequestration and degradation, with implications for energy-dependent proteases.