Conformational and dynamic differences between actin filaments polymerized from ATP- or ADP-actin monomers

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Actin filaments are crucial cytoskeletal components involved in cell structure and motility.
• The nucleotide-bound state (ATP or ADP) of actin monomers influences filament properties.

Purpose of the Study:

• To compare the conformational and dynamic properties of actin filaments polymerized from ATP-actin versus ADP-actin monomers.
• To investigate the role of nucleotide-induced conformational changes in actin filament dynamics.

Main Methods:

• Fluorescence spectroscopy was employed to study actin filaments labeled with IAEDANS at Cys(374).
• Temperature-dependent fluorescence resonance energy transfer (FRET) was used to measure inter-monomer flexibility.
• Radial coordinate calculations assessed the position of Cys(374) relative to the filament axis.

Main Results:

• Filaments from ADP-actin showed lower fluorescence intensity at Cys(374) compared to ATP-actin filaments, indicating a nucleotide-induced conformational change in subdomain 1.
• This conformational change did not alter the radial position of Cys(374).
• Actin filaments assembled from ADP-actin monomers displayed significantly greater inter-monomer flexibility than those from ATP-actin monomers.

Conclusions:

• Nucleotide-bound state (ATP vs. ADP) induces conformational differences in actin monomers, affecting filament dynamics.
• ADP-actin filaments are more flexible than ATP-actin filaments due to altered inter-monomer interactions.
• Phalloidin stabilizes both ATP- and ADP-actin filaments by reducing their flexibility.