Force-activated DNA substrates for probing individual proteins interacting with single-stranded DNA.

Area of Science:

• Biophysics
• Molecular Biology
• Biochemistry

Background:

• Single-molecule force spectroscopy is crucial for understanding protein-DNA interactions.
• Existing methods for creating single-stranded DNA (ssDNA) substrates are often inefficient and labor-intensive.
• Specialized DNA substrates are needed to study protein binding and translocation dynamics.

Purpose of the Study:

• To develop a more efficient and versatile method for generating DNA substrates with single-stranded regions.
• To create a force-activated substrate for controlled generation of ssDNA.
• To enable high-resolution studies of protein-DNA interactions, such as helicase activity.

Main Methods:

• Engineered a DNA construct with a 50%-GC segment lacking adjacent GC pairs, designed to form an internal ssDNA region under force.
• Utilized polymerase chain reaction amplification and site-specific nicking for efficient substrate preparation.
• Developed a complex DNA hairpin adjacent to ssDNA for studying enzyme kinetics.

Main Results:

• Demonstrated a force-activated substrate that generates a ~1000 nucleotide ssDNA region upon partial overstretching (~65 pN).
• Achieved efficient substrate preparation using PCR amplification and nicking.
• Enabled precise temporal control for studying RecQ helicase binding kinetics to ssDNA, revealing a near diffusion-limited reaction.

Conclusions:

• The developed force-activated substrate significantly improves the efficiency and accessibility of creating essential DNA structures for biophysical studies.
• This method facilitates the precise initiation and investigation of critical protein-DNA interactions.
• The approach is broadly applicable to various protein-DNA studies, advancing the field of molecular biophysics.