DNA crossovers and type II DNA topoisomerases: A thermodynamical study

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Eukaryotic type II DNA topoisomerases are essential enzymes that manage DNA topology.
• DNA crossovers are critical structures in DNA recombination and replication.
• Understanding enzyme-crossover interactions is key to DNA repair and genome stability.

Purpose of the Study:

• To theoretically investigate the interaction between tight DNA crossovers and eukaryotic type II DNA topoisomerases.
• To quantitatively analyze the role of type II topoisomerases in DNA strand passage reactions.
• To characterize the formation and stability of enzyme-DNA complexes involving DNA crossovers.

Main Methods:

• Theoretical modeling of enzyme-DNA interactions.
• Quantitative analysis of reaction intermediates and equilibrium constants.
• In vitro biochemical assays to study complex formation.
• Derivation of association constants (KS1, KS2, KS) using published experimental data.

Main Results:

• Tight DNA crossovers are identified as intermediates in the strand-passage reaction.
• A ternary complex (ES1S2) forms between the enzyme and a tight DNA crossover.
• Estimated equilibrium constants suggest a high affinity (KS ≈ 5x10^16 M⁻¹) for the ternary complex, resembling a transition state.
• Covalently crosslinked DNA crossover analogues are predicted to bind with high affinity.

Conclusions:

• The high affinity of the ternary complex supports a protein clamp model for DNA capture by topoisomerases.
• The findings provide insights into the mechanism of DNA strand passage by type II topoisomerases.
• Synthetically modified DNA crossovers could serve as valuable tools for studying topoisomerase function.