Diffusion rate limitations in actin-based propulsion of hard and deformable particles

Area of Science:

• Cell Biology
• Biophysics
• Biochemistry

Background:

• Actin polymerization drives intracellular vesicle and microorganism movement.
• Quantitative studies on biomimetic particles reveal complex motile behaviors.
• Proposed mechanisms include the actoclampin filament end-tracking motor model and the tethered-ratchet model.

Purpose of the Study:

• To model actin monomer diffusion and consumption during actin-based particle propulsion.
• To predict the actin monomer concentration field around motile particles.
• To reconcile observed particle behaviors with proposed motility mechanisms.

Main Methods:

• Development of a mathematical model for actin monomer dynamics.
• Simulation of monomer diffusion and consumption around a moving particle.
• Comparison of model predictions with experimental observations of biomimetic particles.

Main Results:

• The model predicts the actin monomer concentration field around motile particles.
• Load-insensitive, diffusion-limited elongation of (+)-end-tethered actin filaments explains particle propulsion.
• This mechanism quantitatively accounts for saltatory motion of hard particles and oscillatory deformation of soft particles.

Conclusions:

• Actin-based particle propulsion is explained by load-insensitive filament elongation.
• The actoclampin filament-end tracking mechanism is consistent with observed biomimetic particle behaviors.
• The model provides a unified framework for understanding actin-based motility.