Actin filaments as dynamic reservoirs for Drp1 recruitment

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Dynamin-related protein 1 (Drp1) is a GTPase crucial for mitochondrial and peroxisomal fission.
• The precise regulation of Drp1 recruitment to organelles, particularly mitochondria, remains incompletely understood.
• Previous studies indicated a direct interaction between Drp1 and actin filaments, essential for Drp1 oligomerization.

Purpose of the Study:

• To elucidate the complex biophysical properties of the Drp1-actin filament interaction.
• To investigate how factors like nucleotide-bound state, Drp1 concentration, and ionic strength modulate this interaction.
• To assess the physiological relevance of the Drp1-actin binding affinity in cellular contexts.

Main Methods:

• Biochemical assays to characterize Drp1 binding to actin filaments.
• Measurements of Drp1 off-rates and the influence of unbound Drp1.
• Analysis of Drp1 GTPase activity in the presence of varying actin concentrations.
• Determination of Drp1 bundling behavior and its dependence on ionic strength.

Main Results:

• The Drp1-actin interaction exhibits unique dynamics, with unbound Drp1 increasing the off-rate of bound Drp1.
• GDP and GTP differentially affect Drp1-actin binding kinetics, while actin shows a biphasic effect on Drp1 GTP hydrolysis.
• Drp1 can bundle actin filaments, with bundle dynamics and incorporation influenced by ionic strength.
• Measured Drp1-actin binding affinity is physiologically relevant to cellular Drp1 concentrations.

Conclusions:

• Actin filaments provide a dynamic binding platform for Drp1, potentially serving as a reservoir for oligomerization-competent protein.
• The regulated nature of the Drp1-actin interaction offers a mechanism for controlling Drp1 availability for mitochondrial fission.
• Understanding these interactions is key to deciphering the regulation of Drp1-mediated membrane dynamics.