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The fast and the slow: folding and trapping of λ6-85

Maxim B Prigozhin1, Martin Gruebele

  • 1Department of Chemistry and Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, USA.

Journal of the American Chemical Society
|November 10, 2011
PubMed

Insights

Fast protein folding can hide slow kinetic phases, as seen in lambda repressor fragment studies. While the wild-type protein folds quickly, stable mutants and denaturant conditions reveal millisecond traps, suggesting kinetic protection against amyloid formation.

Area of Science:

  • Protein folding kinetics
  • Biophysics
  • Computational biology

Background:

  • Molecular dynamics simulations predicted slow kinetic phases in fast-folding proteins.
  • Lambda repressor fragment λ(6-85) D14A was studied as a model system.

Purpose of the Study:

  • To experimentally investigate the predicted millisecond kinetic phase in λ(6-85) D14A.
  • To understand the role of protein stability and denaturant conditions on folding pathways.

Main Methods:

  • Temperature-jump relaxation experiments were performed to detect kinetics down to 5 milliseconds.
  • Mutants of λ(6-85) with increased stability were synthesized and tested.
  • Mild denaturant conditions were applied to observe effects on folding kinetics.

Main Results:

  • Wild-type λ(6-85) D14A did not exhibit a significant slow kinetic phase.
  • Two more stable mutants of λ(6-85) showed a detectable slow phase.
  • A slow phase for λ(6-85) D14A appeared under mild denaturant conditions.

Conclusions:

  • The study suggests λ(6-85) folds rapidly (microseconds) but can be trapped in compact, β-rich intermediates on a millisecond timescale.
  • These "intramolecular amyloid" traps are kinetically avoided by the wild-type protein but accessible in more stable mutants or denaturing conditions.
  • Protein folding pathways can involve kinetic traps, influencing the protein's ultimate native state and stability.

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