LacI strikes a balance between stability and inducibility.

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.