Fluorescence depolarization studies of filamentous actin analyzed with a genetic algorithm

Area of Science:

• Biophysics
• Computational Biology
• Structural Biology

Background:

• Filamentous actin (F-actin) is a crucial cytoskeletal protein polymer.
• Understanding F-actin's structure and dynamics is essential for cell biology.
• Existing methods for analyzing F-actin structure have limitations.

Purpose of the Study:

• To develop and validate a novel computational method for analyzing fluorescence depolarization data.
• To investigate the local order and reorienting motions of fluorophores attached to F-actin.
• To determine the structural organization of F-actin polymers.

Main Methods:

• Combined genetic algorithm, Brownian dynamics, and Monte Carlo simulations.
• Analyzed fluorescence depolarization data from time-correlated single photon-counting.
• Utilized BODIPY-labeled filamentous actin (F-actin) with fluorophores at cysteine 374 (C374).
• Investigated electronic energy migration within actin polymers.

Main Results:

• The method successfully registered local order and reorienting motions of fluorophores.
• Confirmed the known helical organization of F-actin, validating the technique.
• Observed a shorter-than-expected distance from the filament axis to the fluorophore.
• BODIPY-actin showed a 25-fold more efficient signal for filament formation compared to pyrene-actin.

Conclusions:

• The new computational technique is effective for F-actin structure determination.
• The findings provide insights into fluorophore positioning and dynamics on F-actin.
• BODIPY labeling offers a superior signal for studying actin polymerization kinetics.