Twinfilin bypasses assembly conditions and actin filament aging to drive barbed end depolymerization

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Dynamics

Background:

• Cellular actin networks are crucial for cell structure and function.
• Actin filament assembly primarily occurs at barbed ends, while depolymerization is thought to happen at pointed ends after filament aging.
• High cellular actin monomer concentrations favor assembly, making barbed end depolymerization less likely.

Purpose of the Study:

• To investigate the role of mouse twinfilin in actin filament dynamics.
• To determine if barbed end depolymerization can occur under assembly-promoting conditions.
• To elucidate the mechanism by which twinfilin affects actin filaments.

Main Methods:

• Utilizing microfluidics-assisted total internal reflection fluorescence (TIRF) microscopy.
• Observing single reactions with controlled micromolar concentrations of actin monomers.
• Analyzing the interplay between formin-bound barbed ends and twinfilin-induced depolymerization.

Main Results:

• Mouse twinfilin induces depolymerization of ADP-Pi barbed ends, even with abundant actin monomers present.
• Simultaneous rapid elongation of formin-bound barbed ends and twinfilin-induced depolymerization of free barbed ends were observed.
• Twinfilin facilitates subunit dissociation from ADP-Pi barbed ends, bypassing filament aging.

Conclusions:

• Twinfilin actively disassembles newly polymerized actin filaments by targeting barbed ends.
• This mechanism provides a novel pathway for regulating actin networks independent of filament aging.
• The findings necessitate a re-evaluation of actin depolymerization models in cellular contexts.