An exclusive α/β code directs allostery in TetR-peptide complexes

Area of Science:

• Molecular Biology
• Protein Dynamics
• Biochemistry

Background:

• The allosteric mechanism of the bacterial transcription regulator, tetracycline repressor (TetR), is under scrutiny.
• Recent studies suggest TetR undergoes cooperative folding upon tetracycline binding, rather than conformational switching.

Purpose of the Study:

• To investigate TetR's allosteric mechanism using synthetic peptides that mimic effector molecules.
• To differentiate between proposed allosteric models for TetR function.

Main Methods:

• Structure-function studies using four synthetic peptides designed to interact with TetR.
• Analysis of peptide conformations (β-like vs. α-helical) within the TetR effector binding site.
• Urea-induced unfolding studies and fluorescence measurements to assess protein stability and binding.

Main Results:

• Two inducing peptides adopted a β-like conformation, while two anti-inducing peptides formed an α-helix.
• These distinct binding modes correlated with two specific TetR conformations, one resembling induced TetR and the other the DNA-bound state.
• No increase in thermodynamic stability was observed for peptide-TetR complexes, despite confirmed peptide binding.

Conclusions:

• The bimodal interaction of peptides with TetR supports a classical two-state allosteric model.
• This finding challenges the cooperative folding model for TetR, particularly for these peptide effectors.