Tet repressor induction by tetracycline: a molecular dynamics, continuum electrostatics, and crystallographic study

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The Tet repressor (TetR) is crucial for bacterial resistance against tetracycline (Tc) antibiotics.
• TetR binds operator DNA in the absence of Tc, dissociating upon Tc binding to allow gene expression.
• TetR's precise regulation by Tc makes it valuable in genetic engineering, despite the allosteric signaling distance.

Purpose of the Study:

• To investigate the allosteric mechanism by which tetracycline binding induces TetR dissociation from DNA.
• To elucidate the role of Mg(2+) in the tetracycline-TetR interaction and subsequent conformational changes.
• To validate existing models of TetR allostery using computational simulations and structural data.

Main Methods:

• Molecular dynamics simulations of the TetR:DNA complex and the Tc-bound TetR.
• Continuum electrostatic calculations to analyze binding and dissociation pathways.
• Analysis of crystal structures of TetR to corroborate simulated conformational changes.

Main Results:

• Simulations support a previously inferred allosteric model, revealing detailed molecular interactions.
• Mg(2+) binding to Tc directly and indirectly interacts with TetR helices 8 and 6, initiating structural changes.
• Conformational changes propagate to helix 4, leading to significant N-terminal displacement and reduced DNA binding affinity.

Conclusions:

• Tetracycline acts as a Mg(2+) carrier, with the Mg(2+) ion being key to triggering the allosteric transition in the TetR complex.
• The allosteric mechanism involves a cascade of helix movements initiated by Mg(2+)-TetR interactions, ultimately reducing DNA binding.
• Understanding this mechanism provides insights into TetR function and its utility in biotechnology.