actinsequestering

Actin sequestration is a cellular process where actin monomers or filaments are bound by specific proteins, thereby preventing them from participating in actin polymerization. This mechanism is crucial for regulating the dynamic behavior of the actin cytoskeleton, a network of protein filaments essential for cell shape, movement, and internal transport. Proteins that carry out actin sequestration are known as actin-sequestering proteins.

These proteins bind to actin monomers, often at the barbed (plus) end, preventing them from adding to a growing filament. Alternatively, some sequestering proteins can bind to existing actin filaments, capping their ends and halting further elongation. This control over polymerization is vital for maintaining cellular homeostasis and responding to external stimuli. For instance, during muscle contraction, specific actin-sequestering proteins help regulate the length of actin filaments and their interaction with myosin. In non-muscle cells, actin sequestration plays a role in processes like cell division, cell migration, and the formation of cellular protrusions.

A well-known example of an actin-sequestering protein is profilin. Profilin binds to actin monomers and, while it can prevent their addition to the pointed (minus) end of filaments, it actually facilitates their addition to the barbed end under certain cellular conditions. This complex interaction highlights the nuanced regulatory roles of these proteins. Thymosin beta-4 is another prominent example, which sequesters actin monomers in a 1:1 ratio, thereby maintaining a reservoir of available monomers for rapid polymerization when needed. The activity of actin-sequestering proteins is itself often regulated by other signaling pathways, demonstrating the intricate control over cytoskeletal dynamics.