The effect of diffusion, depolymerization and nucleation promoting factors on actin gel growth

Area of Science:

• Cell Biology
• Biophysics
• Biochemistry

Background:

• Localized actin polymerization drives eukaryotic cell movement.
• Actin monomer diffusion and depolymerization are essential for sustained actin dynamics.
• The bacterial protein ActA facilitates actin-based motility in Listeria monocytogenes.

Purpose of the Study:

• To investigate whether actin monomer diffusion limits actin gel growth.
• To experimentally determine the diffusion coefficient of actin monomers within actin gels.
• To analyze the role of ActA in actin gel formation and its dependence on host cell factors.

Main Methods:

• Formation of actin gels on ActA-coated beads.
• Measurement of actin gel thickness as a function of bead radius.
• Analysis using an elastic model of actin gel growth.
• Qualitative examination of gels formed with ActA fragments and VASP or Arp2/3 complex.

Main Results:

• Actin gel thickness saturates with increasing bead radius, indicating diffusion-limited growth.
• Estimated actin monomer diffusion coefficient within the gel is 2x10(-8) cm(-2) s(-1).
• Depolymerization rates and elastic modulus of actin gels were evaluated.
• Different gel structures were observed with ActA fragments interacting with VASP versus Arp2/3.

Conclusions:

• Actin monomer diffusion significantly restricts actin gel growth, impacting cellular actin dynamics.
• The estimated diffusion coefficient is consistent with values in bulk cytoskeleton.
• ActA-mediated actin gel formation is influenced by interactions with VASP and Arp2/3 complex.