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Assays for the Degradation of Misfolded Proteins in Cells
10:56

Assays for the Degradation of Misfolded Proteins in Cells

Published on: August 28, 2016

Recognition of misfolded proteins by Lon, a AAA(+) protease

Eyal Gur1, Robert T Sauer

  • 1Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Genes & Development
|August 19, 2008
PubMed

Insights

The Lon protease recognizes specific aromatic-rich sequences in unfolded proteins, preventing toxic aggregate formation. This mechanism allows Lon (a AAA+ protease) to degrade damaged proteins while sparing most native structures.

Area of Science:

  • Cellular Biology
  • Protein Degradation
  • Enzymology

Background:

  • Cells constantly experience protein unfolding, particularly under stress.
  • ATP-dependent proteases like Lon are crucial for degrading denatured proteins and preventing toxic aggregation.
  • The precise mechanisms by which Lon distinguishes damaged from functional proteins remain unclear.

Purpose of the Study:

  • To elucidate the substrate recognition mechanism of Escherichia coli Lon protease.
  • To determine how Lon differentiates between unfolded and properly folded proteins.

Main Methods:

  • Investigated substrate binding and degradation using denatured and native proteins with and without specific recognition sequences.
  • Analyzed the role of aromatic residues in Lon recognition.
  • Assessed the impact of protein architecture on Lon substrate preference.

Main Results:

  • Escherichia coli Lon protease specifically recognizes sequences rich in aromatic residues, which are exposed in unfolded polypeptides but buried in native structures.
  • Denatured proteins lacking these aromatic-rich sequences are poor Lon substrates.
  • Lon can also unfold and degrade stably folded proteins if they possess accessible recognition tags.
  • Multiple signals are recognized synergistically, leading to high-affinity binding (nanomolar) to unfolded proteins.

Conclusions:

  • Lon protease utilizes specific sequence motifs, particularly those rich in aromatic residues, for substrate recognition.
  • Protein architecture and the accessibility of these motifs dictate whether Lon degrades a protein independently of its folding status.
  • This recognition mechanism provides a means to discriminate irreversibly damaged proteins from transiently unfolded structures, preventing cellular damage.

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