Theoretical model of membrane protrusions driven by curved active proteins

TL;DR

This paper develops a physical model of membrane protrusions driven by curved active proteins, explaining various cell shape changes including lamellipodia, filopodia, and endocytosis-like structures through simulations.

Contribution

It extends a minimal physical model to include diverse membrane protrusions and complex protein interactions, providing insights into cell shape dynamics.

Findings

Model explains lamellipodia and filopodia formation.

Simulations show complex ruffled clusters and invaginations.

Altered force models mimic bundled cytoskeleton effects.

Abstract

Eukaryotic cells intrinsically change their shape, by changing the composition of their membrane and by restructuring their underlying cytoskeleton. We present here further studies and extensions of a minimal physical model, describing a closed vesicle with mobile curved membrane protein complexes. The cytoskeletal forces describe the protrusive force due to actin polymerization which is recruited to the membrane by the curved protein complexes. We characterize the phase diagrams of this model, as function of the magnitude of the active forces, nearest-neighbor protein interactions and the proteins' spontaneous curvature. It was previously shown that this model can explain the formation of lamellipodia-like flat protrusions, and here we explore the regimes where the model can also give rise to filopodia-like tubular protrusions. We extend the simulation with curved components of both convex and concave species, where we find the formation of complex ruffled clusters, as well as internalized invaginations that resemble the process of endocytosis and macropinocytosis. We alter the force model representing the cytoskeleton to simulate the effects of bundled instead of branched structure, resulting in shapes which resemble filopodia.