Related Experiment Video
Updated: Jun 19, 2026
08:40
Reconstitution of Actin-Based Motility with Commercially Available Proteins
Published on: October 28, 2022
How depolymerization can promote polymerization: the case of actin and profilin.
Elena G Yarmola1, Michael R Bubb
1Department of Medicine, University of Florida, Gainesville, FL 32610, USA. yarmola@ufl.edu
Summary
Profilin regulates actin polymerization, crucial for cell motility. This study reveals how thermal noise and exchange diffusion drive actin polymerization, offering new insights into cell mechanics.
Area of Science:
- Cell Biology
- Biophysics
- Biochemistry
Background:
- Actin filaments undergo rapid polymerization and depolymerization, essential for cell motility and development.
- Profilin, a key actin-binding protein, regulates actin dynamics and interacts with cytoskeletal proteins.
- The precise molecular mechanism of profilin has been debated for over two decades.
Purpose of the Study:
- To discuss established and novel hypotheses on profilin's mechanism of action.
- To explore the role of thermal noise and fluctuation-based processes in cellular events.
- To elucidate the involvement of exchange diffusion in regulating actin polymerization.
Main Methods:
- Literature review of existing hypotheses on profilin function.
- Theoretical analysis of fluctuation-based processes in molecular dynamics.
- Experimental investigation into the role of exchange diffusion in actin polymerization.
Main Results:
- Multiple hypotheses regarding profilin's function are presented and evaluated.
- The significance of thermal noise in molecular processes is highlighted.
- Evidence is provided for the involvement of fluctuation-based exchange diffusion in actin polymerization regulation.
Conclusions:
- Profilin's mechanism involves complex interactions and potentially utilizes thermal fluctuations.
- Exchange diffusion, driven by thermal noise, is a key regulatory process in actin polymerization.
- This work offers a new perspective on actin dynamics and cell motility regulation.
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Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶ nucleation, elongation, and steady-state phase.
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...
01:19Actin Filament Depolymerization
Actin filaments (F-actin) are composed of actin subunits. The dissociation of actin monomers can occur from either end of F-actin. The rate of dissociation is faster from the minus-end or the pointed end, where the actin subunits exist with a bound ADP, together known as ADP-actin. The depolymerization of F-actin is aided by proteins, including the actin-depolymerizing factor (ADF) and cofilin family of proteins, gelsolin, and glia maturation factor (GMF).
In F-actin, the ADF/cofilin proteins...
In F-actin, the ADF/cofilin proteins...
01:11Formation of Higher-order Actin Filaments
The polymerization of G-actin monomers into filamentous F-actin is a multi-step process. Once the F-actins are formed, they can bundle together in different arrangements to form higher-order networks and regulate cellular functions. Common examples include the formation of lamellipodia and filopodia at the cell's leading edge by actin reorganization in a migrating cell. The microvilli on the brush border epithelial cells are also formed through the F-actin network.
The high-order actin networks...
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01:13Actin Polymerization and Cell Motility
Actin is a family of globular proteins that are highly abundant in eukaryotic cells. It makes up approximately 1-5% of total cell protein concentration. Actin monomers polymerize to form a complex network of polarized filaments, the actin cytoskeleton, that plays a crucial role in many cellular processes, including cell motility, division, endocytosis, and metastasis of cancer cells.
Actin cytoskeleton dynamics can produce pushing, pulling, and resistance forces that help the cell to migrate.
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01:18Actin Treadmilling
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01:39Mechanism of Filopodia Formation
Filopodia are thin, actin-rich cellular protrusions that play an important role in many fundamental cellular functions. They vary in their occurrence, length, and positioning in different cell types, suggesting their diverse roles.
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