Crowding alters F-actin secondary structure and hydration

Area of Science:

• Biophysics
• Cell Biology
• Biochemistry

Background:

• Actin filaments are crucial for eukaryotic cell cytoskeleton structure, regulating cell shape and intracellular transport.
• Protein-protein contacts and environmental factors like crowding influence actin filament morphology and biochemical properties.
• The precise effects of crowding on F-actin secondary structure and local environments remain less understood.

Purpose of the Study:

• To investigate the impact of macromolecular crowding and actin filament bundling on the secondary structure and local environments of actin.
• To elucidate how bundling affects the conformational states and hydration of actin filaments.

Main Methods:

• Utilized 2D infrared (2D IR) spectroscopy to analyze actin secondary structure.
• Employed spectral calculations to interpret spectroscopic data and assess local environments.
• Examined isolated filaments, weakly bundled networks, and strongly bundled networks.

Main Results:

• Bundling induces significant alterations in actin's secondary structure, characterized by a reduction in beta-sheet content and an increase in loop conformations.
• Strongly bundled actin networks show decreased backbone solvent exposure and less perturbed alpha-helices.
• Beta-sheets in strongly bundled networks appear nearly 'locked,' while associated loops become less hydrated but remain dynamic.

Conclusions:

• Actin filament bundling alters secondary structure, favoring loop conformations over beta-sheets.
• The observed changes in secondary structure and hydration dynamics are critical for actin network morphology and stability.
• Loop structure plays a key role in governing actin network organization and stability, particularly under crowding conditions induced by agents like PEG.