Base-flipping dynamics in a DNA hairpin processing reaction

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Enzymes accessing DNA substrates often utilize base flipping.
• Understanding the dynamics of multi-step reactions like base flipping remains challenging.
• Crystal structures offer static views, necessitating dynamic biochemical approaches.

Purpose of the Study:

• To investigate the dynamics of base flipping during Tn5 transposition.
• To elucidate the role of DNA bending and probe residues in facilitating base flipping.
• To understand the dual functions of base flipping in DNA processing.

Main Methods:

• Protein-DNA crosslinking
• Potassium permanganate reactivity assays
• Kinetic analysis of DNA nicking and hairpin resolution

Main Results:

• A model was developed where DNA bending and a probe residue drive base flipping.
• Base flipping occurs after the first strand cleavage, relieving DNA tension.
• Eliminating the probe residue reduced nicking kinetics and base flipping by 50%.
• The probe residue is critical for hairpin resolution, acting as a handle for the second strand cleavage.

Conclusions:

• Base flipping is a pivotal step in Tn5 transposition and hairpin processing.
• It facilitates both DNA double helix disruption and precise positioning of DNA for enzymatic cleavage.
• The study provides insights into the dynamic mechanisms of DNA-modifying enzymes.