Microsecond rotational dynamics of actin: spectroscopic detection and theoretical simulation

Area of Science:

• Biophysics
• Molecular Biology
• Protein Dynamics

Background:

• F-actin is a crucial protein in cellular structure and function.
• Understanding F-actin's dynamic properties, including rotational motion, is essential for elucidating its biological roles.
• Previous studies lacked detailed insights into the specific contributions of different types of motion within F-actin.

Purpose of the Study:

• To investigate the microsecond rotational dynamics of F-actin.
• To differentiate between rigid-body rotations and intrafilament bending and twisting motions.
• To establish a methodological foundation for studying F-actin dynamics.

Main Methods:

• Utilized transient phosphorescence anisotropy (TPA) spectroscopy to probe F-actin dynamics.
• Employed a theoretical model developed for DNA dynamics by Schurr and co-workers.
• Constrained model fits using transient absorption anisotropy (TAA) for dye orientation and electron microscopy for filament length distribution.

Main Results:

• The Schurr theory successfully separated torsional flexibility from rigid-body rotations.
• Transient phosphorescence anisotropy decays were primarily attributed to twisting motions within F-actin filaments.
• Rigid-body or bending rotations did not adequately explain the observed TPA decays.

Conclusions:

• F-actin's dynamic properties are best described by continuous elasticity.
• Intrafilament twisting motions are the dominant contributors to microsecond rotational dynamics.
• This study provides a robust method for future investigations into F-actin dynamics and its functional implications.