Actin filament mechanics in the laser trap

Area of Science:

• Biophysics
• Cell Biology
• Biochemistry

Background:

• Actin filaments are essential for numerous cellular functions, including muscle contraction.
• Their mechanical properties, specifically flexural rigidity (EI), are critical for these processes.
• Accurate measurement of actin filament EI is vital for understanding cellular mechanics.

Purpose of the Study:

• To develop and apply a novel method for estimating the flexural rigidity (EI) of actin filaments.
• To investigate the mechanical properties of actin filaments under varying tension.
• To assess the impact of filament bending and microsphere rotation on measurements.

Main Methods:

• Fluorescently labeled actin filaments were attached to microsphere handles.
• Microspheres were captured in independent laser traps, allowing controlled tension application (0-8 pN).
• Filament displacement was measured and analyzed using a physical model accounting for microsphere rotation and filament bending.

Main Results:

• The displacement of microspheres was inconsistent with a rigid filament model, indicating filament bending.
• A novel method estimated actin's flexural rigidity (EI) at approximately 15 x 10^3 pNnm^2.
• Results suggest actin filaments are more compliant than historically assumed.

Conclusions:

• Actin filaments exhibit greater flexibility than previously believed.
• Proper pre-tensioning of actin filaments in laser traps is essential for accurate measurements of molecular events.
• This study provides a new approach to measure actin filament mechanics, impacting our understanding of cellular processes.