Name: actin filament growth and loss
Uploaded: 2023-04-30T10:47:35.000Z
Duration: 1 min 18 s
Channel: JoVE

Actin treadmilling is the continuous addition of G-actin monomers at F-actin&#39;s plus-end and the simultaneous removal from the minus-end. At steady-state, this keeps the filament length unchanged but allows the newly added actin monomers to move forward within the filament.
Treadmilling depends on the critical concentration or Cc of the free monomer, which is the concentration at which the rates of polymerization and depolymerization are equal.
The actin filament grows if the free monomer concentration is higher than the Cc and shrinks if it is lower.
During actin treadmilling, the monomer concentration remains in between the Cc values for the plus and minus-ends, allowing faster and continuous addition of ATP-G-actins only at the plus-end.
These ATP-G-actin monomers undergo gradual ATP hydrolysis with slow phosphate release, resulting in three different forms of actin within F-actin: ATP-actin, ADP-phosphate-actin, and ADP-actin.
The ADP-actins are weakly bound and readily dissociate, resulting in continuous depolymerization at the minus-end of F-actin.

actin treadmilling

Actin Treadmilling

Actin filaments undergo polymerization and depolymerization from either end. The polymerization and depolymerization rates depend on the cytosolic concentration of free G-actins. The polymerization rate is generally higher at the plus or barbed end, while the depolymerization rate is higher at the minus or pointed end. At a steady state, critical concentration describes the concentration of free G-actin monomers at which the polymerization rate at the plus end is equal to that of the depolymerization rate from the minus ends. Actin treadmilling is the continuous addition at one end and dissociation from the other end of the G-actin monomers.&#160;
Actin treadmilling is crucial to several functions in eukaryotic cells, such as cell migration, endocytosis, and exocytosis. Treadmilling occurs continuously, even in resting cells, and is responsible for up to 50% of energy consumption in most cells.
Actin treadmilling depends primarily on three factors,&#160; the ATP hydrolysis rate within the F-actin, the polarity in the polymerization and depolymerization rate at both plus and minus ends, and the cytosolic concentration of free G-actins. ATP-G-Actins bind faster at the plus end and undergo gradual ATP hydrolysis, forming intermittent ADP-Pi-Actins and, eventually, ADP-Actins. ADP-G-actins are loosely associated with the monomers with the F-actins and readily dissociate. At the plus end, the polymerization rate is higher than depolymerization, while at the minus end, the depolymerization rate of G-actin is higher than their polymerization rate. The cytosolic G-actin concentration during the actin treadmilling remains intermediate between that of the critical concentrations of plus and minus ends of F-actin.

Actin filaments undergo polymerization and depolymerization from either end. The polymerization and depolymerization rates depend on the cytosolic ...

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JoVE Core

Cell Biology

Unit 1

The Cytoskeleton I: Actin and Microfilaments

the-cytoskeleton-i-actin-and-microfilaments

KEY TERMS AND CONCEPTS

actin filament growth and loss

Actin filaments grow and shrink at the same time in a process called treadmilling. In this process, G-actin monomers are added at one end of the filament and removed from the other end. The rate of each step depends on the amount of free G-actin in the cytosol, the fluid inside the cell.

The plus end, also called the barbed end, usually adds actin faster. The minus end, also called the pointed end, usually loses actin faster. At steady state, the critical concentration is the level of free G-actin where addition at the plus end matches loss from the minus end.

Treadmilling helps eukaryotic cells carry out important tasks such as cell migration, endocytosis, and exocytosis. It also happens continuously in resting cells. In many cells, it can account for up to 50% of energy use.

Three main factors control this process. These are the ATP hydrolysis rate inside F-actin, the different rates at the plus and minus ends, and the cytosolic level of free G-actin. ATP-bound G-actin binds quickly at the plus end. It then slowly hydrolyzes ATP to form ADP-Pi-actin and later ADP-actin.

ADP-G-actin is loosely attached and leaves the filament more easily. During treadmilling, the G-actin level in the cytosol stays between the critical concentrations for the plus and minus ends. This balance allows actin to keep cycling through growth and loss.

Actin Filament Growth and Loss

introduction to the cytoskeleton

Cytoskeleton Structure and Cell Movement

The cytoskeleton is a network of protein filaments inside the cell. It gives cells shape, helps organize cell contents, and supports movement. Although the name suggests a fixed skeleton, it is a dynamic structure that can change quickly in response to signals or forces. Three main filament types make up the cytoskeleton: microfilaments, microtubules, and intermediate filaments. Each one has different assembly and disassembly behavior, mechanical strength, polarity, and associated motor...

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Cytoskeletal filaments help cells change shape, divide, and move. Their flexibility lets them stay stable for hours during interphase or reorganize quickly during cell division. Strong regulation controls how these filaments assemble, fall apart, and form networks. Microfilaments and microtubules are dynamic, while intermediate filaments are considered more static. Microfilaments are spread throughout the cell body and can shift into different structures. Many proteins in the cell, including...

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intracellular-movement-of-viruses-and-bacteria

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Actin filaments grow and shrink at the same time in a process called treadmilling. In this process, G-actin monomers are added at one end of the filament and removed from the other end. The rate of each step depends on the amount of free G-actin in the cytosol, the fluid inside the cell. The plus end, also called the barbed end, usually adds actin faster. The minus end, also called the pointed end, usually loses actin faster. At steady state, the critical concentration is the level of free...

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generation-of-straight-or-branched-actin-filaments

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actin filament depolymerization

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formation-of-higher-order-actin-filaments

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overview-of-myosin-structure-and-function

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the-role-of-actin-and-myosin-in-non-muscle-cells

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key terms and concepts

Learn how actin filaments keep growing at one end and shrinking at the other, and how ATP hydrolysis and G-actin levels control treadmilling.

Actin Filament Growth and Loss | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Actin Filament Growth and Loss

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