Zero-mode waveguides visualize the first steps during gelsolin-mediated actin filament formation.

Area of Science:

• Cellular Biology
• Biophysics
• Molecular Dynamics

Background:

• Actin filament dynamics are crucial for cellular functions.
• Actin filament elongation is well-understood, but nucleation mechanisms remain elusive.
• Previous studies lacked the resolution to observe single-molecule nucleation dynamics.

Purpose of the Study:

• To elucidate the mechanism of actin filament nucleation at the single-molecule level.
• To investigate the dynamics of gelsolin-mediated actin nucleation.
• To identify factors controlling the initiation of actin filament assembly.

Main Methods:

• Utilized zero-mode waveguides (ZMWs) to achieve attoliter excitation volumes for single-molecule observation.
• Immobilized single gelsolin molecules as nucleators within ZMWs.
• Monitored early-stage actin filament assembly dynamics in real-time.

Main Results:

• Observed a dynamic nucleation process with two distinct actin dimer populations.
• These populations dictate the probability of subsequent filament elongation.
• Inhibiting actin flattening (a conformational change) prevented elongation, highlighting its necessity.

Conclusions:

• Gelsolin-mediated actin nucleation is a dynamic process involving pathway competition.
• A conformational transition in actin is essential for filament formation.
• The stability of actin dimers plays a critical role in initiating filament assembly.