Multiple supramolecular structures formed by interaction of actin with protamine

Area of Science:

• Biochemistry
• Biophysics
• Materials Science

Background:

• Actin polymerization is crucial for cellular processes.
• Protamine is a DNA-binding protein with potential interactions with actin.
• Understanding protein-protein interactions is key to cellular mechanics.

Purpose of the Study:

• To investigate the supramolecular structures formed by protamine-actin interactions.
• To analyze the effect of protamine on actin's exchange dynamics.
• To elucidate the role of ionic strength and molar ratios in complex formation.

Main Methods:

• Varying molar ratios of protamine to G-actin and F-actin.
• Adjusting ionic strength (low and high, including Tyrode solution).
• Filtration using 0.45 μm Millipore filters to separate complexes.
• Studying exchange reactions of actin-protamine complexes.

Main Results:

• Protamine induces diverse actin structures (globular, extended, threads, ropes) dependent on conditions.
• High ionic strength leads to rope-like structures of 4-5nm diameter filaments.
• Protamine addition to F-actin causes filament breakage and decreased viscosity.
• Actin-protamine complexes exhibit varying exchange rates with free actin, influenced by Mg2+ and ATPase activity.

Conclusions:

• Protamine significantly alters actin's supramolecular organization and dynamics.
• The exchange rate of actin within protamine complexes is modulated by ionic strength and Mg2+.
• Protamine-actin complexes may influence actin's functional properties, potentially involving ATP/ADP exchange on bound G-actin.