Tying a molecular knot with optical tweezers

Area of Science:

• Biophysics
• Molecular Biology
• Materials Science

Background:

• Cellular filamentous structures like actin and microtubules are crucial for mechanical functions.
• The mechanical properties of filaments, such as DNA flexibility, are vital for biological processes.
• Previous mechanical characterization methods lacked precise control over filament shape.

Purpose of the Study:

• To develop a method for controlled manipulation of molecular filament curvature.
• To investigate the mechanical behavior of knotted filaments, specifically actin and DNA.
• To explore curvature-dependent interactions with proteins for DNA.

Main Methods:

• Utilized optical tweezers to manipulate the ends of molecular strands (actin and DNA).
• Introduced controlled curvature by tying knots in the filaments.
• Measured filament breakage force and analyzed the effect of knot diameter on mechanical properties.

Main Results:

• Actin filaments break at knots when the diameter is less than 0.4 micrometers, with a breakage force of approximately 1 pN.
• The flexural rigidity of actin filaments remained constant even at small diameters.
• Knotted DNA was found to be stronger than knotted actin, opening avenues for studying DNA-protein interactions.

Conclusions:

• Tying knots provides a method for continuous control over the radius of curvature of molecular filaments.
• Actin filaments exhibit significantly reduced strength at sharp bends induced by knots.
• This technique allows for the investigation of curvature-dependent phenomena in biopolymers like DNA.