Cyclase-associated protein interacts with actin filament barbed ends to promote depolymerization and formin...

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Cyclase-associated protein (CAP) is crucial for cellular actin dynamics.
• Its precise molecular mechanisms, particularly at filament ends, remain incompletely understood.
• Previous work implicated the N terminus in pointed-end depolymerization with cofilin.

Purpose of the Study:

• To elucidate the role of the C terminus of CAP in actin filament dynamics.
• To investigate CAP's interaction with actin monomers and other regulatory proteins like profilin.
• To understand the domain-specific functions of CAP in actin turnover.

Main Methods:

• In vitro microfluidics-assisted total internal reflection fluorescence (TIRF) microscopy.
• Site-directed mutagenesis and structural modeling.
• Biochemical assays measuring actin filament depolymerization and growth rates.

Main Results:

• The C terminus of CAP (CAP1 and CAP2) accelerates depolymerization at barbed ends of actin filaments.
• WH2 and CARP domains are essential for CAP's barbed-end depolymerization activity.
• CAP directly interacts with profilin to cooperatively enhance barbed-end depolymerization.
• CAP1 inhibits barbed-end growth and promotes formin dissociation in the presence of actin monomers.

Conclusions:

• CAP utilizes distinct domains and mechanisms to regulate both barbed and pointed ends of actin filaments.
• CAP and profilin exhibit cooperative regulation of actin dynamics through direct interaction.
• Actin barbed ends are dynamic regulatory sites involving complex protein competition and cooperation.