Tropomyosin isoforms regulate cofilin 1 activity by modulating actin filament conformation

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Tropomyosin (TPM) and cofilin are key regulators of actin filament dynamics.
• Different TPM isoforms exhibit distinct effects on cofilin 1 activity, influencing actin polymerization and depolymerization.
• TPM1 products stabilize actin filaments, while TPM3 products promote cofilin-dependent severing.

Purpose of the Study:

• To investigate the conformational changes in actin filaments induced by tropomyosin and cofilin 1 binding.
• To elucidate the specific sites of interaction and regulation at the actin filament interface.
• To understand how tropomyosin isoforms differentially modulate cofilin 1's effect on actin structure.

Main Methods:

• Utilized skeletal actin and yeast wild type/mutant actins (Q41C, S265C).
• Employed F-actin cross-linking and fluorescence labeling (acrylodan at Cys41/Cys265) to study conformational changes.
• Performed tryptic digestion of F-Mg-actin and FRET analysis with AEDANS labeling.

Main Results:

• Tropomyosin isoforms differentially regulated cofilin-induced conformational changes at actin filament longitudinal and lateral interfaces.
• Tryptic digestion confirmed isoform-specific regulation of actin-actin interface alterations by cofilin.
• No significant conformational changes were observed in the actin C-terminal segment across conditions.

Conclusions:

• Actin's D-loop and H-loop are critical sites for tropomyosin isoform-mediated regulation of cofilin activity.
• Differential regulation of actin-cofilin interactions by tropomyosin isoforms impacts filament dynamics.
• These findings provide insights into the molecular mechanisms governing actin cytoskeleton organization.