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LacI strikes a balance between stability and inducibility.

Jinwen Yuan1, Malin Lüking1, Spartak Zikrin1

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Mutations in the lac repressor (LacI) hinge region affect DNA binding stability and specificity. The study reveals a trade-off between binding strength and inducibility, not search speed.

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Area of Science:

  • Molecular Biology
  • Biophysics
  • Genetics

Background:

  • Transcription factors (TFs) locate DNA via diffusion and sliding.
  • TF conformational switching balances search and binding.
  • LacI hinge helices are crucial for conformational changes.

Purpose of the Study:

  • Investigate how hinge region mutations impact LacI search speed and binding.
  • Determine the relationship between LacI binding stability, specificity, and inducibility.

Main Methods:

  • Molecular dynamics simulations to select LacI mutants.
  • In vitro DNA microarray binding kinetics assays.
  • In vivo single-molecule experiments.

Main Results:

  • One mutation increased specificity but decreased binding strength.
  • Another mutation increased binding strength but decreased specificity.
  • Impaired LacI dissociation from DNA upon IPTG induction for the strong binder.
  • Altered specificity had less impact on search time than expected.

Conclusions:

  • The trade-off in LacI is between binding stability and inducibility.
  • Conformational switching impacts DNA binding kinetics and response to induction.