Liquid-like condensates mediate competition between actin branching and bundling

Area of Science:

• Cell Biology
• Biophysics

Background:

• Cellular actin networks are crucial for cell motility, involving a balance between actin branching and bundling.
• Steric hindrance between branched actin filaments can impede bundling.
• Previously, liquid-like protein condensates were shown to catalyze either branching or bundling, but not both simultaneously.

Approach:

• Investigated the interplay between actin branching and bundling within multi-component protein condensates.
• Added the actin branching nucleator, Arp2/3 complex, to condensates of the actin bundling protein, VASP.
• Examined how varying actin to VASP ratios affects filament organization.

Key Points:

• At low actin to VASP ratios, Arp2/3-mediated branching inhibited VASP-driven bundling, consistent with simulations.
• At higher actin to VASP ratios, Arp2/3 addition induced aster-shaped structures with bundled filaments emerging from a branched core.
• These structures mimic cellular formations like filopodia emerging from lamellipodial networks.

Conclusions:

• Multi-component, liquid-like protein condensates can dynamically modulate the competition between actin branching and bundling.
• These condensates can organize higher-order actin structures relevant to cell motility.
• The ratio of branching to bundling proteins within condensates dictates the emergent morphology.