Tetracycline repressor allostery does not depend on divalent metal recognition.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Tetracycline resistance genes in bacteria are regulated by TetR repressors.
• Tetracycline antibiotics, complexed with magnesium, induce TetR allosteric changes, releasing it from DNA.
• Previous studies suggested magnesium binding is critical for TetR induction.

Purpose of the Study:

• To investigate the role of magnesium in TetR allosteric regulation by 5a,6-anhydrotetracycline.
• To resolve the paradox of 5a,6-anhydrotetracycline inducing TetR without magnesium.

Main Methods:

• Determined crystal structures of TetR-5a,6-anhydrotetracycline complexes.
• Complexes were formed in the presence of magnesium, EDTA, or potassium.

Main Results:

• TetR-5a,6-anhydrotetracycline complex structures were analyzed under varying metal conditions.
• Binding of 5a,6-anhydrotetracycline induced similar allosteric effects, regardless of metal presence.
• The induction mechanism was indistinguishable from canonical tetracycline induction.

Conclusions:

• Magnesium recognition is not a prerequisite for TetR allosteric regulation.
• The proposed metal-free induction mode for 5a,6-anhydrotetracycline is not supported.
• TetR allostery can be triggered by tetracycline derivatives independently of magnesium.