actin polymerization or depolymerization

Definition

Target type: biologicalprocess

Assembly or disassembly of actin filaments by the addition or removal of actin monomers from a filament. [GOC:mah]

Actin polymerization and depolymerization are essential cellular processes that dynamically regulate the structure and function of the cytoskeleton. Actin, a globular protein, assembles into long, filamentous polymers called F-actin, which form a network that provides structural support, enables cell motility, and facilitates intracellular transport. The dynamic interplay between polymerization and depolymerization is tightly controlled by various regulatory proteins and signaling pathways.

**Actin Polymerization:**

* **Nucleation:** The process initiates with the formation of a small oligomer of actin monomers called a nucleus. This nucleation step is slow and energetically unfavorable, often requiring the assistance of nucleation-promoting factors (NPFs) like formins or Arp2/3 complex.
* **Elongation:** Once a nucleus forms, actin monomers rapidly add to both ends of the filament, leading to filament elongation. The barbed end (plus end) of the filament grows faster than the pointed end (minus end) due to differences in monomer binding affinity.
* **Monomer Binding:** Actin monomers bind to the filament in an ATP-bound state. ATP hydrolysis to ADP occurs after monomer incorporation, and this transition is crucial for filament dynamics.

**Actin Depolymerization:**

* **Monomer Dissociation:** ADP-bound actin monomers at the pointed end of the filament can dissociate, leading to filament shortening. This process is promoted by depolymerizing factors like cofilin.
* **Capping:** Proteins like capping proteins can bind to the ends of actin filaments, preventing further monomer addition or dissociation, effectively "capping" the filament.
* **Severing:** Proteins like gelsolin can sever existing actin filaments, creating new ends that can then be capped or further polymerized.

**Regulation of Actin Dynamics:**

* **Regulatory Proteins:** A diverse array of proteins control the rates of polymerization and depolymerization by interacting with actin monomers and filaments. These proteins include:
* **Formins:** Nucleate and elongate filaments.
* **Arp2/3 complex:** Nucleates branched filaments.
* **Cofilin:** Promotes depolymerization.
* **Capping proteins:** Block filament ends.
* **Severing proteins:** Break filaments.
* **Signaling Pathways:** Cellular signaling pathways, including those involving Rho GTPases, can regulate actin dynamics by modulating the activity of regulatory proteins.

**Functional Implications:**

* **Cell Motility:** Actin polymerization and depolymerization drive the movement of cells, including amoeboid movement and cell migration.
* **Cytokinesis:** During cell division, actin filaments form a contractile ring that divides the cytoplasm into two daughter cells.
* **Vesicle Transport:** Actin filaments provide tracks for the movement of vesicles and organelles within the cell.
* **Muscle Contraction:** Actin filaments interact with myosin to generate force in muscle contraction.

In summary, the dynamic interplay between actin polymerization and depolymerization is essential for maintaining the structural integrity and functional capabilities of cells. This dynamic process is tightly controlled by a complex network of regulatory proteins and signaling pathways, allowing cells to adapt to changing environments and perform essential biological functions.'
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Proteins (1)

Compounds (15)