How ATP hydrolysis controls filament assembly from profilin-actin: implication for formin processivity.

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• Formins are key regulators of actin filament dynamics.
• Profilin-actin interactions are crucial for actin assembly but not fully understood.
• The role of nucleotide hydrolysis in profilin-actin assembly is unclear.

Purpose of the Study:

• To elucidate the mechanism of actin filament assembly from profilin-actin at formin-bound barbed ends.
• To investigate the influence of nucleotide state on profilin-actin interactions.
• To determine the coupling of ATP hydrolysis to profilin-actin assembly.

Main Methods:

• Analysis of actin assembly at free and formin-bound barbed ends.
• Use of ADP and non-hydrolyzable CrATP to study nucleotide states.
• Quantitative modeling of actin assembly kinetics.

Main Results:

• Profilin caps barbed ends in ADP and CrATP/ADP-Pi states, with higher affinity when formin is bound.
• Profilin accelerates depolymerization of ADP-F-actin, enhanced by formin.
• A model was developed where ATP hydrolysis and Pi release from the penultimate subunit are necessary for profilin release and elongation.
• Formin processivity depends on profilin release from actin.

Conclusions:

• Actin filament elongation from profilin-actin requires ATP hydrolysis and Pi release.
• Formin facilitates processive elongation by managing profilin release.
• Formin's role is to utilize profilin for processive barbed-end elongation, not to alter profilin's intrinsic activity.