Human cofilin forms oligomers exhibiting actin bundling activity

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• Human cofilin is a key regulator of actin dynamics.
• Cofilin's known function involves severing actin filaments.
• The potential for cofilin self-association and its functional consequences are not fully understood.

Purpose of the Study:

• To investigate the self-association properties of human cofilin.
• To characterize the biological activity of cofilin dimers and oligomers.
• To explore the in vivo relevance of cofilin's monomeric and oligomeric forms.

Main Methods:

• Chemical cross-linking (water-soluble carbodiimide, Ellman's reagent, glutathione disulfide) to induce cofilin self-association.
• Biochemical assays to measure changes in F-actin viscosity and light-scattering.
• Electron microscopy to visualize cofilin-actin structures.
• Reversal of disulfide bonds using dithiothreitol.

Main Results:

• Human cofilin readily forms dimers and oligomers via intermolecular disulfide bonds (Cys39, Cys147).
• Cofilin dimers/oligomers exhibit actin bundling activity, increasing viscosity and light-scattering, distinct from monomeric cofilin's actin severing.
• Oligomer-induced actin bundles resemble cellular actin-cofilin rods; bundling is reversible to severing.
• Oligomerization is favored at pH 8, enhanced by phosphatidylinositol 4,5-bisphosphate, and occurs with actin.

Conclusions:

• Human cofilin exists in at least two functional states: monomeric (actin severing) and oligomeric (actin bundling).
• Oligomerization, potentially regulated by local concentration and protein interactions, may stabilize cofilin's bundling function in vivo.
• These findings provide insight into cofilin's dual role in regulating actin dynamics under physiological and stress conditions.