actin rod assembly

Definition

Target type: biologicalprocess

The assembly of actin rods, a cellular structure consisting of parallel, hexagonally arranged actin tubules. [GOC:pg, PMID:14706699]

Actin rod assembly is a fundamental process in eukaryotic cells, essential for diverse cellular functions like cell migration, division, and maintaining cell shape. The process involves the polymerization of monomeric globular actin (G-actin) into filamentous actin (F-actin) to form rod-like structures. The formation of actin rods is regulated by a complex interplay of actin-binding proteins, including nucleators, capping proteins, and severing factors.

**Nucleation:** The initial step in actin rod assembly is the formation of a stable nucleus, typically a trimer of G-actin molecules. Nucleation is the rate-limiting step in actin polymerization and requires specific proteins called nucleators. These proteins, such as the Arp2/3 complex, formin, and Spire, provide a platform for G-actin monomers to bind and initiate the formation of the nucleus.

**Elongation:** Once the nucleus is formed, G-actin monomers add to both ends of the filament, a process called elongation. This step is driven by the inherent ability of G-actin to bind to other G-actin molecules and is further influenced by the concentration of free G-actin monomers. The plus end of the filament, also known as the barbed end, grows faster than the minus end, known as the pointed end.

**Capping:** To control the length of the actin rods, cells utilize capping proteins that bind to the ends of the filament. Capping proteins, such as CapZ and tropomodulin, prevent further addition of G-actin monomers to the ends, effectively capping the filament.

**Severing:** To regulate the length and organization of actin rods, cells use severing factors like cofilin. Cofilin binds to F-actin, destabilizing the filament and promoting its breakage into shorter fragments. This process allows for the recycling of actin and the generation of new filaments for further polymerization.

**Branching:** In many cell types, actin filaments form branched networks. The Arp2/3 complex is crucial for this process, as it binds to the side of existing filaments and nucleates the formation of new branches at a 70-degree angle. These branched networks provide structural support and create a dynamic cytoskeleton, allowing cells to respond to their environment and migrate.

**Regulation:** Actin rod assembly is tightly regulated by a complex interplay of signaling pathways, including those involving Rho GTPases. These small GTPases, such as Rho, Rac, and Cdc42, activate downstream effectors that influence the activity of actin-binding proteins, thereby controlling the dynamics of actin polymerization and the formation of specific actin structures.

**Conclusion:** The assembly of actin rods is a multifaceted process that is essential for diverse cellular functions. The intricate interplay of nucleators, capping proteins, severing factors, and regulatory pathways ensures that actin polymerization occurs in a controlled manner, leading to the formation of dynamic and functional actin structures.'
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Proteins (1)

Compounds (22)