Twinfilin is a non-processive depolymerase which synergizes with formin to dramatically accelerate actin filament...

Area of Science:

• Cellular biology
• Biochemistry
• Molecular dynamics

Background:

• Conventional understanding posits actin filament disassembly occurs primarily at pointed ends via depolymerization.
• Twinfilin's role in actin dynamics is debated, with suggestions of barbed-end depolymerization, monomer sequestration, and capping/uncapping activities.
• The precise mechanisms by which twinfilin influences barbed-end dynamics remain unclear.

Purpose of the Study:

• To elucidate the multifunctional roles of twinfilin at actin filament barbed ends.
• To investigate twinfilin's impact on actin depolymerization, capping, and uncapping dynamics.
• To clarify twinfilin's interaction with formin in regulating barbed-end dynamics.

Main Methods:

• Utilized multicolor single-molecule microscopy to observe twinfilin-actin interactions.
• Quantified binding kinetics and depolymerization rates of twinfilin at barbed ends.
• Assessed the synergistic effects of twinfilin and formin on filament uncapping.

Main Results:

• Demonstrated that both mouse and yeast twinfilin act as non-processive depolymerases, transiently interacting with barbed ends and removing 1-2 subunits per event.
• Showed twinfilin synergizes with formin to accelerate the uncapping of barbed ends capped by cyclase-associated protein (CP) by up to 320-fold.
• Found that twinfilin-mediated uncapping is dependent on filament nucleotide state, with less enhancement on newly assembled filaments.

Conclusions:

• Established twinfilin as a multifunctional barbed-end binding protein.
• Highlighted twinfilin's novel roles in non-processive depolymerization and transient capping of actin filaments.
• Confirmed twinfilin's capacity to synergize with formin for rapid actin filament barbed-end uncapping.