Sodium fluoride as a nucleating factor for Mg-actin polymerization.

Area of Science:

• Biochemistry
• Cell Biology
• Biophysics

Background:

• Actin filament dynamics are crucial for cellular processes.
• Fluoride compounds like beryllium fluoride and aluminum fluoride stabilize actin filaments.
• The role of magnesium fluoride in actin functional activities was previously unknown.

Purpose of the Study:

• To investigate the effect of sodium fluoride (NaF) on actin polymerization and filament dynamics.
• To explore the potential role of magnesium fluoride in NaF-induced actin assembly.
• To determine if NaF promotes actin assembly independently of the RhoA pathway.

Main Methods:

• Assembly of Mg-F-actin using proteolytically cleaved actin monomers (Pln-actin).
• Assessing ATPase activity and sedimentation of Pln-F-actin.
• Investigating nucleotide binding cleft accessibility and D-loop protection.
• Observing F-actin assembly in cultured cells under inhibited RhoA pathway activity.

Main Results:

• Sodium fluoride (NaF) significantly accelerates polymerization of Mg-F-actin by stabilizing nuclei.
• NaF did not inhibit ATPase activity or increase Pln-F-actin sedimentation.
• NaF diminished nucleotide binding cleft accessibility and protected the D-loop, indicating stabilized longitudinal contacts.
• NaF promoted F-actin assembly in cultured cells even when the RhoA pathway was inhibited.

Conclusions:

• Sodium fluoride (NaF) promotes actin filament assembly, primarily by stabilizing nuclei during polymerization.
• The observed effects suggest magnesium fluoride, formed from NaF and bound magnesium, plays a key role in NaF-induced actin assembly.
• NaF can directly induce actin filament assembly in cells, independent of RhoA signaling, highlighting a novel regulatory mechanism.