Steady state dynamics of a moving model cell.

Cell movement is a complex process influenced by the organization of actin filaments. Prior research has shown that actin treadmilling at the leading edge is essential for crawling. However, the precise balance of branching and capping proteins remains unclear. This gap motivated the investigation into how these proteins regulate actin dynamics. No prior work had resolved how branching and capping rates affect cell velocity. Understanding these interactions could clarify how cells maintain steady motility. It was already known that Arp2/3 and capZ/Gelsolin are involved in actin regulation. But the exact interplay between these proteins is still uncertain. This uncertainty drove the need for computational modeling of actin concentration profiles.

The aim of this work is to explore how branching and capping proteins influence actin dynamics during cell movement. The specific problem is understanding how these proteins affect the velocity of a moving cell. The motivation is to identify optimal rates for branching and capping that maximize cell speed. The study also seeks to determine how capping affects nucleation of new filaments. Researchers propose that Arp2/3 and capping proteins may have antagonistic roles. This antagonism could explain how treadmilling is maintained. The study focuses on the functional relationship between these proteins. The goal is to simulate actin concentration profiles and compare them to experimental data.

The researchers used computer simulations to model actin dynamics in a moving cell. They computed steady state concentration profiles for globular and filamentous actin. These profiles were compared to experimentally observed data for validation. The simulations included branching of new filaments via Arp2/3 and capping of existing filaments. The model incorporated parameters for capping and branching rates. The velocity of the model cell was measured under different rate conditions. The simulations tracked how these rates affect overall cell movement. The approach allowed for testing various combinations of branching and capping rates.

The simulations revealed an optimal capping and branching rate that maximizes cell velocity. At this rate, the actin network maintains steady motility. The model showed that capping increases nucleation of new filaments via Arp2/3 branching. This finding aligns with a recently proposed monomer gating model. The results suggest that capping and branching rates are interdependent. The velocity of the model cell peaks at specific rate combinations. The actin concentration profiles matched experimental observations closely. The simulations also showed functional antagonism between Arp2/3 and capping proteins.

The authors propose that optimal branching and capping rates are crucial for cell velocity. Their simulations suggest that capping enhances nucleation via Arp2/3-induced branching. The findings support the monomer gating model for actin dynamics. The antagonism between Arp2/3 and capping proteins is a key insight. The model cell's velocity is maximized at specific rate combinations. The agreement between simulated and experimental profiles is significant. The study highlights the importance of rate balance in actin treadmilling. These results may help refine models of actin network regulation.